[media] tea575x: fix HW seek

Fix HW seek in TEA575x to work properly:
- a delay must be present after search start and before first register read
  or the seek does weird things
- when the search stops, the new frequency is not available immediately, we
  must wait until it appears in the register (fortunately, we can clear the
  frequency bits when starting the search as it starts at the frequency
  currently set, not from the value written)
- sometimes, seek remains on the current frequency (or moves only a little),
  so repeat it until it moves by at least 50 kHz

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>