media: atomisp: remove an impossible condition

Changeset dc9f65cf ("media: staging: atomisp: avoid a warning if 32
bits build") was meant to solve an impossible condition when building
with 32 bits. It turns that this impossible condition also happens wit
64 bits:
	drivers/staging/media/atomisp/platform/intel-mid/atomisp_gmin_platform.c:698 gmin_get_config_var() warn: impossible condition '(*out_len > (~0)) => (0-u64max > u64max)'

After a further analysis, this condition will always be false as, on
all architectures, size_t doesn't have more bits than unsigned long.

Also, the only two archs that really matter are x86 and x86_64, as this
driver doesn't build on other archs (as it depends on X86-specific UEFI
support).

So, just drop the useless code.

Fixes: dc9f65cf ("media: staging: atomisp: avoid a warning if 32 bits build")

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>