[AMDGPU][MC] Corrected handling of "-" before expressions

See bug 41156: https://bugs.llvm.org/show_bug.cgi?id=41156

Reviewers: artem.tamazov, arsenm

Differential Revision: https://reviews.llvm.org/D60622

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358596 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed