[media] si2157: return -EINVAL if firmware blob is too big

A previous patch added a check if the firmware is too big, but it didn't
set the return error code with the right value.

[mchehab@osg.samsung.com: I ended by applying a v1 of Laura's patch, without
 the proper return code. This patch contains the difference between v2 and v1 of
 the Laura's "si2157: Bounds check firmware" patch]
Cc: stable@kernel.org
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Reviewed-by: Olli Salonen <olli.salonen@iki.fi>
Tested-by: Olli Salonen <olli.salonen@iki.fi>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>