[AMDGPU][MC] Corrected handling of negative expressions

See bug 35716: https://bugs.llvm.org/show_bug.cgi?id=35716

Reviewers: artem.tamazov, arsenm

Differential Revision: https://reviews.llvm.org/D41488

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321372 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed