gpiolib: fix typo in comment

This fixes an off-by-one error in a comment.
Signed-off-by: NMichael Buesch <mb@bu3sch.de>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/gpio.h

@@ -13,7 +13,7 @@
  *
  * While the GPIO programming interface defines valid GPIO numbers
  * to be in the range 0..MAX_INT, this library restricts them to the
- * smaller range 0..ARCH_NR_GPIOS.
+ * smaller range 0..ARCH_NR_GPIOS-1.
  */
 
 #ifndef ARCH_NR_GPIOS