[XFS] Make xfsbufd threads freezable

Fix breakage caused by commit 83144186
that did not introduce the necessary call to set_freezable() in
xfs/linux-2.6/xfs_buf.c .

SGI-PV: 974224
SGI-Modid: xfs-linux-melb:xfs-kern:30203a
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

fs/xfs/linux-2.6/xfs_buf.c

@@ -1743,6 +1743,8 @@ xfsbufd(
 
 	current->flags |= PF_MEMALLOC;
 
+	set_freezable();
+
 	do {
 		if (unlikely(freezing(current))) {
 			set_bit(XBT_FORCE_SLEEP, &target->bt_flags);