greybus: loopback: Drop NULL check on container_of pointer

container_of cannot return NULL and the pointer passed to this context uses
reference counter bumped inside a spinlock, so the base pointer will be
valid at this point.
Suggested-by: Johan Hovold <johan@hovoldconstulting.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/loopback.c

@@ -526,9 +526,6 @@ static void gb_loopback_async_operation_work(struct work_struct *work)
 	struct gb_loopback_async_operation *op_async;
 
 	op_async = container_of(work, struct gb_loopback_async_operation, work);
-	if (!op_async)
-		return;
-
 	gb = op_async->gb;
 	operation = op_async->operation;