xfs: kill xfs_fs_mount_cmn_err() macro

The xfs_fs_mount_cmn_err() hides a simple check as to whether the
mount path should output an error or not. Remove the macro and open
code the check.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>