[AMDGPU] Assembler: fix v_mac_f16 immediates

Reviewers: vpykhtin, artem.tamazov, tstellarAMD

Subscribers: arsenm, kzhuravl, wdng, nhaehnle, yaxunl, tony-tye

Differential Revision: https://reviews.llvm.org/D28802

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292224 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed