xfs: only clear the suid bit once in xfs_write

file_remove_suid already calls into ->setattr to clear the suid and
sgid bits if needed, no need to start a second transaction to do it
ourselves.

Note that xfs_write_clear_setuid issues a sync transaction while the
path through ->setattr doesn't, but that is consistant with the
other filesystems.

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