[X86][AVX] Limit getFauxShuffleMask INSERT_SUBVECTOR support to 2 inputs

rL343853 didn't limit the number of subinputs, but we don't currently support faux shuffles with more than 2 total inputs, so put a limiter in place until this is fixed.

Found by Artem Dergachev.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343891 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed