[AMDGPU] SIInstrInfo: Fix resultDependsOnExec for VOPC instructions (#134629)
SIInstrInfo::resultDependsOnExec assumes that operand 0 of a comparison
is always the destination of the instruction. This is not true for
instructions in VOPC form where it is "src0". This led to a crash in
machine-cse.
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Co-authored-by: Matt Arsenault <arsenm2@gmail.com>