[media] em28xx: don't treat device as webcam if an unknown sensor is detected

With an unknown sensor, norm_maxw() and norm_maxh() return 0 as max.
height and width values, which causes a devide by zero in size_to_scale().
Of course we could use speculative default values for unknown sensors,
but the chance that the device works at this resolution without any
driver/setup is very low and therefore not worth the efforts.
Instead, just don't treat the device as camera.
A message will then be printed to the log that the device isn't supported.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/em28xx/em28xx-cards.c

@@ -2919,7 +2919,9 @@ static void em28xx_card_setup(struct em28xx *dev)
 	 * If sensor is not found, then it isn't a webcam.
 	 */
 	if (dev->board.is_webcam) {
-		if (em28xx_detect_sensor(dev) < 0)
+		em28xx_detect_sensor(dev);
+		if (dev->em28xx_sensor == EM28XX_NOSENSOR)
+			/* NOTE: error/unknown sensor/no sensor */
 			dev->board.is_webcam = 0;
 	}
 
@@ -3667,9 +3669,11 @@ static int em28xx_usb_probe(struct usb_interface *interface,
 		try_bulk = usb_xfer_mode > 0;
 	}
 
-	/* Disable V4L2 if the device doesn't have a decoder */
+	/* Disable V4L2 if the device doesn't have a decoder or image sensor */
 	if (has_video &&
-	    dev->board.decoder == EM28XX_NODECODER && !dev->board.is_webcam) {
+	    dev->board.decoder == EM28XX_NODECODER &&
+	    dev->em28xx_sensor == EM28XX_NOSENSOR) {
+
 		dev_err(&interface->dev,
 			"Currently, V4L2 is not supported on this model\n");
 		has_video = false;