[X86][SSE] Minor fix to VPBLENDW AVX2 commutation.

D6015 / rL221313 enabled commutation for SSE immediate blend instructions, but due to a typo the AVX2 VPBLENDW ymm instructions weren't flagged as commutative along with the others in the tables, but were still being commuted in code and tested for.

llvm-svn: 225612