[AArch64] Fix an assertion for pre-index generation with unscaled loads/stores.

Differential Revision: https://reviews.llvm.org/D36248
PR34035

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310066 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed