drm/crtc: Fix potential NULL pointer dereference

drm_property_create_blob() could return NULL in which case NULL pointer
dereference error (on connector->edid_blob_ptr) is possible. Return if
connector->edid_blob_ptr is NULL.

Fixes the following smatch error:
drivers/gpu/drm/drm_crtc.c:3186 drm_mode_connector_update_edid_property()
error: potential null dereference 'connector->edid_blob_ptr'.
(drm_property_create_blob returns null)
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -3191,6 +3191,8 @@ int drm_mode_connector_update_edid_property(struct drm_connector *connector,
 	size = EDID_LENGTH * (1 + edid->extensions);
 	connector->edid_blob_ptr = drm_property_create_blob(connector->dev,
 							    size, edid);
+	if (!connector->edid_blob_ptr)
+		return -EINVAL;
 
 	ret = drm_connector_property_set_value(connector,
 					       dev->mode_config.edid_property,