Fix for Solidisk Sideways RAM

[monkeyman79]

Write to RAM bank selected by User VIA output port B even if bank selected by &FE30 is writable.

Testing:

• Start with default Model B configuration
• Enable "SW RAM Board"
• Configure banks C-F as RAM, check "Allow SW RAM Write" for those banks
• Move basic2 and dnfs to e.g. banks 8 and 9
• Run Solidisk Sideways RAM utils vol 1 (it can be downloaded from here: https://stardot.org.uk/forums/download/file.php?id=3340)
• Without the patch, the menu program crashes (older version that I have doesn't crash but only displays one bank available)
• With the patch, the menu program correctly displays "4 Sideways Ram Banks Available"

This is related to #70

[chrisn]

Thank you!