Fix the bug when handling shufflevector for aarch64.

Summary: This Fixes https://bugs.llvm.org/show_bug.cgi?id=33600

Reviewers: mssimpso, davidxl, Carrot

Reviewed By: mssimpso

Subscribers: aemerson, rengolin, sanjoy, javed.absar, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D34641

llvm-svn: 306334