irqchip/eznps: Drop pointless static qualifier in nps400_of_init()

There is no need to have the 'struct irq_domain *nps400_root_domain'
variable static since new value is always assigned before use.

Fixes: 44df427c

 ("irqchip: add nps Internal and external irqchips")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1476714417-12095-1-git-send-email-weiyj.lk@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>