drm/exynos: Make 'drm_hdmi_get_edid' static

Fixes the following warning:
drivers/gpu/drm/exynos/exynos_drm_hdmi.c:111:13: warning:
symbol 'drm_hdmi_get_edid' was not declared. Should it be static?
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_hdmi.c

@@ -108,7 +108,7 @@ static bool drm_hdmi_is_connected(struct device *dev)
 	return false;
 }
 
-struct edid *drm_hdmi_get_edid(struct device *dev,
+static struct edid *drm_hdmi_get_edid(struct device *dev,
 			struct drm_connector *connector)
 {
 	struct drm_hdmi_context *ctx = to_context(dev);