sgi-xpc: ensure flags are updated before bte_copy

sgi-xpc: ensure flags are updated before bte_copy

commit 69b3bb65fa97a1e8563518dbbc35cd57beefb2d4 upstream.

The clearing of the msg->flags needs a barrier between it and the notify
of the channel threads that the messages are cleaned and ready for use.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>