[PATCH] drivers/mfd/sm501.c: fix an off-by-one

Fix an off-by-one spotted by the Coverity checker.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Vincent Sanders <vince@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>