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

As reported by Coverity, there's a potential risk of a division
by zero on some calls to jpeg_set_qual(), if quality is zero.

As quality can't be 0 or lower than that, adds an extra clause
to cover this special case.

Coverity reports: CID#11922280, CID#11922293, CID#11922295
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/gspca/jpeg.h

@@ -154,7 +154,9 @@ 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;