AMDGPU/SI: Fix crash on physical registers in SIInstrInfo::isOperandLegal()

No test case for this.  I ran into it while working on some improvements
to SIShrinkInstructions.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241816 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed