drm/exynos: Make g2d_pm_ops static

Fixes the following warning:
drivers/gpu/drm/exynos/exynos_drm_g2d.c:897:1: warning:
symbol 'g2d_pm_ops' was not declared. Should it be static?
Signed-off-by: NSachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_g2d.c

@@ -894,7 +894,7 @@ static int g2d_resume(struct device *dev)
 }
 #endif
 
-SIMPLE_DEV_PM_OPS(g2d_pm_ops, g2d_suspend, g2d_resume);
+static SIMPLE_DEV_PM_OPS(g2d_pm_ops, g2d_suspend, g2d_resume);
 
 struct platform_driver g2d_driver = {
 	.probe		= g2d_probe,