[AArch64] Fix use of a regex in the win-alloca.ll test. NFC.

Check that the variable actually is the same as the one previously
matched.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327107 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed