drivers/char/rio/rioctrl.c: off by one error in rioctrl.c

If DownLoad.ProductCode == MAX_PRODUCT, that would be a problem when we do
RIOBootTable[DownLoad.ProductCode] a couple lines down.

Found by smatch (http://repo.or.cz/w/smatch.git).

Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>