[AMDGPU] Fix typo in implicit operand lists

Several tests had a typo where they mentioned sgpr17 twice instead of
sgpr17 and sgpr27. This had a significant effect on the
"scavenge_sgpr_pei_no_sgprs" tests because there was actually an sgpr
available, namely sgpr27.

Differential Revision: https://reviews.llvm.org/D100960