Overrun in drivers/char/rio/riocmd.c

This got somehow lost in the noise.  This fixes coverity bug id #1025, if
Rup is greater or equal to MAX_RUP, we run past the Mapping Array.

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Cc: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>