V4L/DVB: uvcvideo: Prevent division by 0 when control step value is 0

The control step values reported by the device are used as a divisor
unchecked, which can result in a division by zero.

Check the step value and make it 1 when null.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/uvc/uvc_ctrl.c

@@ -1071,6 +1071,8 @@ int uvc_ctrl_set(struct uvc_video_chain *chain,
 				   uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX));
 		step = mapping->get(mapping, UVC_GET_RES,
 				    uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES));
+		if (step == 0)
+			step = 1;
 
 		xctrl->value = min + (xctrl->value - min + step/2) / step * step;
 		xctrl->value = clamp(xctrl->value, min, max);