[media] stk-webcam: Delete an unnecessary check before the function call "vfree"

The vfree() function performs also input parameter validation.
Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: NMarkus Elfring <elfring@users.sourceforge.net>
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/stkwebcam/stk-webcam.c

@@ -556,10 +556,8 @@ static int stk_free_sio_buffers(struct stk_camera *dev)
 	nbufs = dev->n_sbufs;
 	dev->n_sbufs = 0;
 	spin_unlock_irqrestore(&dev->spinlock, flags);
-	for (i = 0; i < nbufs; i++) {
-		if (dev->sio_bufs[i].buffer != NULL)
-			vfree(dev->sio_bufs[i].buffer);
-	}
+	for (i = 0; i < nbufs; i++)
+		vfree(dev->sio_bufs[i].buffer);
 	kfree(dev->sio_bufs);
 	dev->sio_bufs = NULL;
 	return 0;