[media] uvcvideo: Fix reading the current exposure value of UVC

V4L2_CID_EXPOSURE_ABSOLUTE property does not return an updated value when
autoexposure (V4L2_CID_EXPOSURE_AUTO) is turned on. This patch fixes this
issue by adding the UVC_CTRL_FLAG_AUTO_UPDATE flag.

Tested on a C920 camera.
Signed-off-by: Anton V. Shokurov <shokurov.anton.v@yandex.ru>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/uvc/uvc_ctrl.c

@@ -227,7 +227,8 @@ static struct uvc_control_info uvc_ctrls[] = {
 		.size		= 4,
 		.flags		= UVC_CTRL_FLAG_SET_CUR
 				| UVC_CTRL_FLAG_GET_RANGE
-				| UVC_CTRL_FLAG_RESTORE,
+				| UVC_CTRL_FLAG_RESTORE
+				| UVC_CTRL_FLAG_AUTO_UPDATE,
 	},
 	{
 		.entity		= UVC_GUID_UVC_CAMERA,