[media] adv7604: set restart_stdi_once flag when signal is lost

If the restart_stdi_once trick fails to find a valid
format the flag was never reset.

Signed-off-by: Martin Bugge <marbugge@cisco.com>
Cc: Mats Randgaard <matrandg@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>