media: staging: atomisp: avoid a warning if 32 bits build

Checking if a size_t value is bigger than ULONG_INT only makes
sense if building on 64 bits, as warned by:
	drivers/staging/media/atomisp/platform/intel-mid/atomisp_gmin_platform.c:697 gmin_get_config_var() warn: impossible condition '(*out_len > (~0)) => (0-u32max > u32max)'

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>