arm: Replace various irq_desc accesses

Use the proper functions. There is no need to fiddle with irq_desc.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org&gt;C>
Acked-by: Tony Lindgren <tony@atomide.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: arm <linux-arm-kernel@lists.infradead.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Link: http://lkml.kernel.org/r/20140223212737.099151500@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>