arm: Use genirq lockdep helper to set lock class

Remove the open coded access to irq_desc which will fail on sparse irq
and use the proper wrappers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/arm/mach-at91/gpio.c b/arch/arm/mach-at91/gpio.c
index af818a2..5abcfc0 100644
--- a/arch/arm/mach-at91/gpio.c
+++ b/arch/arm/mach-at91/gpio.c
@@ -518,7 +518,7 @@
 		__raw_writel(~0, this->regbase + PIO_IDR);
 
 		for (i = 0, pin = this->chip.base; i < 32; i++, pin++) {
-			lockdep_set_class(&irq_desc[pin].lock, &gpio_lock_class);
+			irq_set_lockdep_class(pin, &gpio_lock_class);
 
 			/*
 			 * Can use the "simple" and not "edge" handler since it's