[DAGCombiner] Fix an off-by-one error in vector logic

Without this, we could end up trying to get the Nth (0-indexed) element
from a subvector of size N.

Differential Revision: https://reviews.llvm.org/D37880


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314380 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed