[Power9][NFC]Make pre-inc-disable case more robust

With some patch adopted for Power9 vabsd* insns, some CHECKs can't get the expected results.
But it's false alarm, we should update the case more robust.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349325 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed