[media] tvp5150: Replace container_of() with to_tvp5150()

Use the driver-specific inline function to cast from a subdev pointer to
a tvp5150 pointer instead of the generic container_of().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>