[media] tef6862: clamp frequency

Clamp the frequency to the valid frequency range as per the V4L2 specification.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Richard Röjfors <richard.rojfors@pelagicore.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>