[media] em28xx: remove field tuner_addr from struct em28xx

The tuner address is only used by the v4l submodule and at tuner setup and
can be obtained from the board data directly (if specified).

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>