irqchip: exynos-combiner: call handle_bad_irq directly

This patch is inspired from following commit aec00956
(irqchip: gic: Call handle_bad_irq() directly)

Also this will help in removing unwanted inclusion
of header file "asm/mach/irq.h"

Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>