irqchip: spear_shirq: Simplify register access code

The extra register data structure is pointless. Move the offsets of
the status and the mask register into the shirq block structure.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20140619212713.923306179@linutronix.de


Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>