media: atmel-isc: Make local symbol fmt_configs_list static

Fixes the following sparse warning:

drivers/media/platform/atmel/atmel-isc.c:338:19: warning:
 symbol 'fmt_configs_list' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Wenyou Yang <wenyou.yang@microchip.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>