Fix DSP CMPAR disassembly

Previously the two operand register selection bits were inverted, causing "CMPAR AC1, AX0.H" to be disassembled as "CMPAR AC0, AX1.H".

DSP RE is always fun: on the one hand Nintendo does a lot of stupid shit, so anything weird could be a legitimate bug of the UCode that is not supposed to make any sense. On the other hand, Dolphin *also* does a lot of stupid shit, so there's always that doubt.

Note: completely untested change - done with the GH text editor, just to show you how much I care :) . These operand descriptions are only used for disassembly, so no real behavior change is expected.