[media] pvrusb2-io: no need to check if sp is not NULL

The buffer_complete() routine assumes that sp is not NULL,
otherwise it will fail completely. Btw, this is also
assumed at pvr2_buffer_queue(), with is the routine that
setups the URB handling.

So, remove the bogus for the callback at buffer_complete.

This fix this smatch warning:
	drivers/media/usb/pvrusb2/pvrusb2-io.c:476 buffer_complete() warn: variable dereferenced before check 'sp' (see line 472)
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/pvrusb2/pvrusb2-io.c

@@ -473,7 +473,7 @@ static void buffer_complete(struct urb *urb)
 	}
 	spin_unlock_irqrestore(&sp->list_lock,irq_flags);
 	pvr2_buffer_set_ready(bp);
-	if (sp && sp->callback_func) {
+	if (sp->callback_func) {
 		sp->callback_func(sp->callback_data);
 	}
 }