xfs: kill suid/sgid through the truncate path.

xfs: kill suid/sgid through the truncate path.

commit 2962f5a5dcc56f69cbf62121a7be67cc15d6940b upstream.

XFS has failed to kill suid/sgid bits correctly when truncating
files of non-zero size since commit c4ed4243 ("xfs: split
xfs_setattr") introduced in the 3.1 kernel. Fix it.

Fix it.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
(cherry picked from commit 56c19e89b38618390addfc743d822f99519055c6)
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>