[ARM] 4557/1: Fix PXA irq gpio initialization

As pointed out by Jrgen, we are overflowing the number of GPIOs
in pxa_init_irq_gpio(). I'm seeing the same problem on my HTC
Universal PXA270 based PDA.
According to Eric, the function argument is the number of GPIOs,
so we should keep the semantics and reduce the number of
iteration by 1.

Signed-off-by: Samuel Ortiz <sameo@openedhand.com>
Acked-by: Jrgen Schindele <linux@schindele.name>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>