irqchip: exynos-combiner: Staticize combiner_init

combiner_init() is referenced only in this file. Make it
static.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kgene.kim@samsung.com
Cc: t.figa@samsung.com
Cc: arnd@arndb.de
Cc: patches@linaro.org
Link: http://lkml.kernel.org/r/1372246597-32323-2-git-send-email-sachin.kamat@linaro.org


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>