drm/nouveau: fix null pointer dereference in nouveau_connector_get_modes

In nouveau_connector_get_modes(), the return value of drm_mode_duplicate()
is assigned to mode, which will lead to a possible NULL pointer
dereference on failure of drm_mode_duplicate(). Add a check to avoid npd.

Cc: [email protected]
Fixes: 6ee7386 ("drm/nouveau: Add DRM driver for NVIDIA GPUs")
Signed-off-by: Ma Ke <[email protected]>
Signed-off-by: Lyude Paul <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Ma Ke

drivers/gpu/drm/nouveau/nouveau_connector.c

@@ -1001,6 +1001,9 @@ nouveau_connector_get_modes(struct drm_connector *connector)
 		struct drm_display_mode *mode;
 
 		mode = drm_mode_duplicate(dev, nv_connector->native_mode);
+		if (!mode)
+			return 0;
+
 		drm_mode_probed_add(connector, mode);
 		ret = 1;
 	}