ARM: exynos: Fix warning due to missing 'inline' in stub

In file included from arch/arm/mach-exynos/clock-exynos5.c:29:0:
arch/arm/mach-exynos/common.h:28:12: warning: 'exynos_pm_late_initcall' defined but not used [-Wunused-function]

Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Shawn Guo <shawn.guo@linaro.org>