Fix a QoI bug reported by a user.

Set the source location for the "member reference base type ... is not a
structure or union" diag to point at the operator rather than the member name.
If we're giving this diagnostic because of a typo'd '.' in place of a ';' at
the end of a line, the caret previously pointed at the identifier on the
following line, which isn't as helpful as it could be. Pointing the caret at
the '.' makes it more obvious what the problem is.

llvm-svn: 155267