irqchip/bcm2836: Make code more readable

Avoid using hardcoded magics. We have a #define for this number.
No functional changes.

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Lee Jones <lee@kernel.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-rpi-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1451166444-11044-5-git-send-email-eric@anholt.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/irqchip/irq-bcm2836.c

@@ -167,7 +167,7 @@ __exception_irq_entry bcm2836_arm_irqchip_handle_irq(struct pt_regs *regs)
 	u32 stat;
 
 	stat = readl_relaxed(intc.base + LOCAL_IRQ_PENDING0 + 4 * cpu);
-	if (stat & 0x10) {
+	if (stat & BIT(LOCAL_IRQ_MAILBOX0)) {
 #ifdef CONFIG_SMP
 		void __iomem *mailbox0 = (intc.base +
 					  LOCAL_MAILBOX0_CLR0 + 16 * cpu);