V4L/DVB (4203): Explicitly set the enum values.

It's better to use explicit enums. It reduces the chance of someone
inserting new enums in the middle which would break things.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>