ARM: EXYNOS: no duplicate mask/unmask in eint0_15

chained_irq_enter/exit() already mask&ack/unmask the chained interrupt.
There is no need to also explicitly do it in the handler.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Acked-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>