virtio: fix suspend when using virtio_balloon

Break out of wait_event_interruptible() if freezing has been requested,
in the vballoon thread. Without this change vballoon refuses to stop and
the system can't suspend.

Signed-off-by: Marcelo Tosatti <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>
Cc: [e-mail]

drivers/virtio/virtio_balloon.c

···
 		try_to_freeze();
 		wait_event_interruptible(vb->config_change,
 					 (diff = towards_target(vb)) != 0
-					 || kthread_should_stop());
+					 || kthread_should_stop()
+					 || freezing(current));
 		if (diff > 0)
 			fill_balloon(vb, diff);
 		else if (diff < 0)