[AArch64] Fix UB about shift amount exceeds data bit-width

Summary:
Fixes an UB caught by sanitizer. The shift amount might be larger than 32 so the operand should be 1ULL.
In this patch,  we replace the original expression with  existing API with uint64_t type.

Reviewers: eli.friedman, rengolin

Reviewed By: rengolin

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

Differential Revision: https://reviews.llvm.org/D44234

llvm-svn: 326969