drm/gma500: fix psb_intel_lvds_mode_valid()'s return type

The method struct drm_connector_helper_funcs::mode_valid is defined
as returning an 'enum drm_mode_status' but the driver implementation
for this method, psb_intel_lvds_mode_valid(), uses an 'int' for it.

Fix this by using 'enum drm_mode_status' for psb_intel_lvds_mode_valid().
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180424131458.2060-1-luc.vanoostenryck@gmail.com

drivers/gpu/drm/gma500/psb_intel_drv.h

@@ -255,7 +255,7 @@ extern int intelfb_remove(struct drm_device *dev,
 extern bool psb_intel_lvds_mode_fixup(struct drm_encoder *encoder,
 				      const struct drm_display_mode *mode,
 				      struct drm_display_mode *adjusted_mode);
-extern int psb_intel_lvds_mode_valid(struct drm_connector *connector,
+extern enum drm_mode_status psb_intel_lvds_mode_valid(struct drm_connector *connector,
 				     struct drm_display_mode *mode);
 extern int psb_intel_lvds_set_property(struct drm_connector *connector,
 					struct drm_property *property,

drivers/gpu/drm/gma500/psb_intel_lvds.c

@@ -343,7 +343,7 @@ static void psb_intel_lvds_restore(struct drm_connector *connector)
 	}
 }
 
-int psb_intel_lvds_mode_valid(struct drm_connector *connector,
+enum drm_mode_status psb_intel_lvds_mode_valid(struct drm_connector *connector,
 				 struct drm_display_mode *mode)
 {
 	struct drm_psb_private *dev_priv = connector->dev->dev_private;