sh/irq: Use irq accessor functions instead of open coded access

This is a preparatory patch for refactoring the internals if irq_data.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20150713151626.616384365@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>