[AMDGPU] Fix illegal shrink of V_SUBB_U32 and V_ADDC_U32

If there is an immediate operand we shall not shrink V_SUBB_U32
and V_ADDC_U32, it does not fit e32 encoding.

Differential Revison: https://reviews.llvm.org/D34291

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305840 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed