[AsmParser] Suppress compile warning for targets with no register diags

This fixes the "switch statement contains 'default' but no 'case' labels"
warnings in table-generated code introduced in r315295.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315571 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed