To avoid printing out multiple error messages for cases like:

To avoid printing out multiple error messages for cases like:

.long 80+08

go ahead and assume that if we've got an Error token that we handled it
already. Otherwise if it's a token we can't handle then go ahead and
return the default error.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129322 91177308-0d34-0410-b5e6-96231b3b80d8