[media] gpsca: remove the risk of a division by zero

As reported by Peter Kovar, there's a potential risk of a division by
zero on calls to jpeg_set_qual() when quality is zero.

As quality can't be 0 or lower than that, add an extra clause to cover
this special case.
Signed-off-by: Luis de Bethencourt <luis.bg@samsung.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/gspca/topro.c

@@ -969,7 +969,9 @@ static void jpeg_set_qual(u8 *jpeg_hdr,
 {
 	int i, sc;
 
-	if (quality < 50)
+	if (quality <= 0)
+		sc = 5000;
+	else if (quality < 50)
 		sc = 5000 / quality;
 	else
 		sc = 200 - quality * 2;