[media] siano: Fix array boundary at smscore_translate_msg()

As reported by Dan Carpenter:
	FYI, there are new smatch warnings show up in

	tree:   git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next master
	head:   da17d7bda957ae4697b6abc0793f74fb9b50b58f
	commit: 4c3bdb5e2f5612ceb99ac17dbbe673b59a94d105 [media] siano: better debug send/receive messages

	drivers/media/common/siano/smscoreapi.c:396 smscore_translate_msg() error: buffer overflow 'siano_msgs' 401 <= 401

While it is almost impossible for this error to happen in
practice, as it would require the siano's firmware to return
an special invalid answer to a message request, fixing it
is trivial. So, let's do it.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>