ARM: OMAP4: Fix array size for irq_target_cpu

If NR_IRQS is less than MAX_IRQS, we end up writing past the
irq_target_cpu array in omap_wakeupgen_init():

/* Associate all the IRQs to boot CPU like GIC init does. */
for (i = 0; i < max_irqs; i++)
	irq_target_cpu[i] = boot_cpu;

This can happen if SPARSE_IRQ is enabled as by default NR_IRQS is
set to 16. Without this patch we're overwriting other data during
the boot.

Cc: stable@vger.kernel.org
Signed-off-by: Tony Lindgren <tony@atomide.com>