[AMDGPU] Fix default value of glc for mubuf rtn atomics

Mubuf rtn atomics use GLC_1 thus default value for glc operand
should be -1, see https://reviews.llvm.org/D90730.
This allows us to report error when rtn atomic requires glc=1
but does not have glc operand in input.

Differential Revision: https://reviews.llvm.org/D92654