[media] atmel-isc: Fix the static checker warning

Initialize the pointer 'fmt' before the start of
the loop.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Songjun Wu <songjun.wu@microchip.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>