[ARM] 4680/1: parentheses around NR_IRQS definition

If NR_IRQS is defined as a sum without surrounding parentheses, this may
lead to problems when used in multiplications. This may lead to problems
in:
arch/ia64/sn/kernel/irq.c:516
arch/x86/kernel/io_apic_32.c:693, 694, 699, 700
fs/proc/proc_misc.c:464

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>