[ARM, Asm] Fix ubsan failure caused by out-of-range enum value

[ARM, Asm] Fix ubsan failure caused by out-of-range enum value

In this code, we use ~0U as a sentinel value for any operand class that doesn't
have a user-friendly error message, but this value isn't in range of the
MatchClassKind enum, so we need to ensure it does not get passed to isSubclass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314793 91177308-0d34-0410-b5e6-96231b3b80d8