[RTL] fixed control_merge.vhd

[shundroid]

I'm working on adding a spec bit on each RTL module. I found that the current control_merge.vhd didn't work, so I fixed this.

Note: control_merge.vhd will be referenced by the dataless version of control_merge with a spec bit, as it treats the extra bit as 1-bit data.

[shundroid]

But it may be used if we want to combine extra bits (including the speculative bit) with control tokens (just note!)