[AArch64] Skip isZIPMask check for masks with an odd number of elements.

[AArch64] Skip isZIPMask check for masks with an odd number of elements.

We process 2 elements at a time and expect the number of elements to be
even. Similar to D60690.

Reviewers: dmgreen, samparker, t.p.northover

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D65400

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@367831 91177308-0d34-0410-b5e6-96231b3b80d8