[media] tlg2300: fix frequency handling

The usual set of problems: the frequency isn't clamped to the frequency range,
no tuner index check and the frequency isn't initialized properly on module
load.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>