ceph: update the time stamps and try to drop the suid/sgid

ceph: update the time stamps and try to drop the suid/sgid

The fallocate will try to clear the suid/sgid if a unprevileged user
changed the file.

There is no POSIX item requires that we should clear the suid/sgid
in fallocate code path but this is the default behaviour for most of
the filesystems and the VFS layer. And also the same for the write
code path, which have already support it.

And also we need to update the time stamps since the fallocate will
change the file contents.

Cc: stable@vger.kernel.org
Link: https://tracker.ceph.com/issues/58054
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>