irqchip: gic: print correct resume irq name

Currently hwirq number is used to get descriptor for irq
in gic_show_resume_irq function which returns incorrect
irq descriptor.

Update it to use correct irq number using irq_find_mapping.

Change-Id: Ib61ebcb3d5e520566b157ee5781d11b70d0f513d
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>