ARM: EXYNOS: Constify local exynos_pmu_data structure

The Exynos5420 instance of exynos_pmu_data structure is not modified and
can be made const.
Suggested-by: Pavel Fedin <p.fedin@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Pankaj Dubey <pankaj.dubey@samsung.com>

arch/arm/mach-exynos/pmu.c

@@ -880,7 +880,7 @@ static const struct exynos_pmu_data exynos5250_pmu_data = {
 	.powerdown_conf	= exynos5_powerdown_conf,
 };
 
-static struct exynos_pmu_data exynos5420_pmu_data = {
+static const struct exynos_pmu_data exynos5420_pmu_data = {
 	.pmu_config	= exynos5420_pmu_config,
 	.pmu_init	= exynos5420_pmu_init,
 	.powerdown_conf	= exynos5420_powerdown_conf,