AMDGPU: Fix not preserving CSR VGPR if used for SGPR spills

Before this was not done if the function had no calls in it. This
is still a possible issue with any callable function, regardless
of calls present.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328659 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed