V4L/DVB (12750): em28xx: fix unused variable warning

Remove unused variable from when I introduced the g_std() function.

This work was sponsored by EyeMagnet Limited.
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-video.c

@@ -1144,7 +1144,6 @@ static int vidioc_g_std(struct file *file, void *priv, v4l2_std_id *norm)
 {
 	struct em28xx_fh   *fh  = priv;
 	struct em28xx      *dev = fh->dev;
-	struct v4l2_format f;
 	int                rc;
 
 	rc = check_dev(dev);