irqchip: spear_shirq: Remove the parent irq "ack"/unmask

"ack" is actually a mask in the parent irq. The demultiplexer and the
handlers run with interrupts disabled. No point in masking and
unmasking the parent.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20140619212713.754300980@linutronix.de


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