V4L/DVB (4222): Always switch tuner mode when calling VIDIOC_S_FREQUENCY.

Fixes the weird and incorrect condition in VIDIOC_S_FREQUENCY.
The tuner should always be switched to the mode specified in the
v4l2_frequency struct. Much simpler and also corresponding to the
v4l2 specification.
The old condition made it impossible to switch from radio to
analog tv mode using VIDIOC_S_FREQUENCY. Instead the (tv) frequency would
be given to the radio tuner.

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