V4L/DVB (3437): Fix typo in enum name and use enum in struct dmxdev_filter

Rename 'enum dmxdevype' to 'enum dmxdev_type' and use this enum instead
of int for the member 'type' of struct dmxdev_filter.

Signed-off-by: Andreas Oberritter <obi@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>