[media] atmel-isc: set the format on the first open

Set the current format on the first open.

Signed-off-by: Songjun Wu <songjun.wu@microchip.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>