ARM IAS: fix diagnostics of improper qualification

An improper qualifier would result in a superfluous error due to the parser not
consuming the remainder of the statement.  Simply consume the remainder of the
statement to avoid the error.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199035 91177308-0d34-0410-b5e6-96231b3b80d8