staging: comedi: ni_660x: fix memory barrier without comment

Fix the checkpatch.pl issue. Move the memory barrier to a better place.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_660x.c

@@ -613,9 +613,11 @@ static irqreturn_t ni_660x_interrupt(int irq, void *d)
 
 	if (!dev->attached)
 		return IRQ_NONE;
+	/* make sure dev->attached is checked before doing anything else */
+	smp_mb();
+
 	/* lock to avoid race with comedi_poll */
 	spin_lock_irqsave(&devpriv->interrupt_lock, flags);
-	smp_mb();
 	for (i = 0; i < dev->n_subdevices; ++i) {
 		s = &dev->subdevices[i];
 		if (s->type == COMEDI_SUBD_COUNTER)