Fix warnings -Wfloat-conversion, -Wimplicit-float-conversion

[rbuj]

CFLAGS="-g -O0 -Wconversion -Wunused-macros -Wunused-parameter" CC=clang ./autogen.sh --prefix=/usr --enable-debug --enable-compile-warnings=maximum && make &> make.log

Fix the build warnings below:

gvc-balance-bar.c:485:76: warning: implicit conversion loses floating-point precision: 'gdouble' (aka 'double') to 'gfloat' (aka 'float') [-Wimplicit-float-conversion]
                mate_mixer_stream_control_set_balance (bar->priv->control, value);
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                      ^~~~~
gvc-balance-bar.c:488:73: warning: implicit conversion loses floating-point precision: 'gdouble' (aka 'double') to 'gfloat' (aka 'float') [-Wimplicit-float-conversion]
                mate_mixer_stream_control_set_fade (bar->priv->control, value);
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                      ^~~~~
gvc-balance-bar.c:493:55: warning: implicit conversion turns floating-point number into integer: 'gdouble' (aka 'double') to 'guint' (aka 'unsigned int') [-Wfloat-conversion]
                                                      value);
                                                      ^~~~~
--
gvc-level-bar.c:182:55: warning: implicit conversion turns floating-point number into integer: 'double' to 'int' [-Wfloat-conversion]
                peak_level = bar->priv->peak_fraction * bar->priv->layout.area.height;
                           ~ ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gvc-level-bar.c:183:54: warning: implicit conversion turns floating-point number into integer: 'double' to 'int' [-Wfloat-conversion]
                max_peak_level = bar->priv->max_peak * bar->priv->layout.area.height;
                               ~ ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gvc-level-bar.c:192:55: warning: implicit conversion turns floating-point number into integer: 'double' to 'int' [-Wfloat-conversion]
                peak_level = bar->priv->peak_fraction * bar->priv->layout.area.width;
                           ~ ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gvc-level-bar.c:193:54: warning: implicit conversion turns floating-point number into integer: 'double' to 'int' [-Wfloat-conversion]
                max_peak_level = bar->priv->max_peak * bar->priv->layout.area.width;
                               ~ ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
gvc-level-bar.c:527:24: warning: implicit conversion turns floating-point number into integer: 'double' to '_Bool' [-Wfloat-conversion]
        if (!width || !height)
                      ~^~~~~~
gvc-level-bar.c:527:14: warning: implicit conversion turns floating-point number into integer: 'double' to '_Bool' [-Wfloat-conversion]
        if (!width || !height)
            ~^~~~~

[lukefromdc]

Note that our new developers who are writing many PR's to fix so many of these warnings need to be reviewing each other's PR's. This would break the logjam and clear the backlog. They are the future of MATE as many of the older devs cannot make a lifetime commitment, and cannot review a dozen PR's a day on a production line basis. The bigger DE's get financial help from distros, we don't get that.