[media] tvp5150: identify it as a MEDIA_ENT_F_ATV_DECODER

The tvp5150 is an analog TV decoder. Identify as such at
the media graph, or otherwise devices using it would fail.

That avoids the following warning:
	[ 1546.669139] usb 2-3.3: Entity type for entity tvp5150 5-005c was not initialized!

Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>