[media] media: fix au0828 compile error from au0828_boards initialization

au0828 picked up UNSET from videobuf-core.h and fails to compile
if videobuf-core.h isn't included. Change it to use -1U instead
to fix the problem.

    drivers/media/usb/au0828/au0828-cards.c:47:17: error: ‘UNSET’ undeclared here (not in a function)
       .tuner_type = UNSET,

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/au0828/au0828-cards.c

@@ -44,7 +44,7 @@ static void hvr950q_cs5340_audio(void *priv, int enable)
 struct au0828_board au0828_boards[] = {
 	[AU0828_BOARD_UNKNOWN] = {
 		.name	= "Unknown board",
-		.tuner_type = UNSET,
+		.tuner_type = -1U,
 		.tuner_addr = ADDR_UNSET,
 	},
 	[AU0828_BOARD_HAUPPAUGE_HVR850] = {