drm/rockchip: cdn-dp-core: Make cdn_dp_core_suspend/resume static

This fixes the following warning detected when running make with W=1

    drivers/gpu/drm/rockchip//cdn-dp-core.c:1112:5: warning: no previous
    prototype for ‘cdn_dp_suspend’ [-Wmissing-prototypes]

    drivers/gpu/drm/rockchip//cdn-dp-core.c:1126:5: warning: no previous
    prototype for ‘cdn_dp_resume’ [-Wmissing-prototypes]
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200426161653.7710-1-enric.balletbo@collabora.com

drivers/gpu/drm/rockchip/cdn-dp-core.c

@@ -1106,7 +1106,7 @@ static const struct component_ops cdn_dp_component_ops = {
 	.unbind = cdn_dp_unbind,
 };
 
-int cdn_dp_suspend(struct device *dev)
+static int cdn_dp_suspend(struct device *dev)
 {
 	struct cdn_dp_device *dp = dev_get_drvdata(dev);
 	int ret = 0;
@@ -1120,7 +1120,7 @@ int cdn_dp_suspend(struct device *dev)
 	return ret;
 }
 
-int cdn_dp_resume(struct device *dev)
+static int cdn_dp_resume(struct device *dev)
 {
 	struct cdn_dp_device *dp = dev_get_drvdata(dev);