[IRTranslator] Simplify error handling for translating constants. NFC.

We don't need to check whether the fallback path is enabled to return
false. Just do that all the time on error cases, the caller knows (or
at least should know!) how to handle the failing case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297535 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed