drm/gma500: fix null pointer dereference in psb_intel_lvds_get_modes

In psb_intel_lvds_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: 89c7813 ("gma500: Add Poulsbo support")
Signed-off-by: Ma Ke <[email protected]>
Signed-off-by: Patrik Jakobsson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Ma Ke

drivers/gpu/drm/gma500/psb_intel_lvds.c

@@ -504,6 +504,9 @@ static int psb_intel_lvds_get_modes(struct drm_connector *connector)
 	if (mode_dev->panel_fixed_mode != NULL) {
 		struct drm_display_mode *mode =
 		    drm_mode_duplicate(dev, mode_dev->panel_fixed_mode);
+		if (!mode)
+			return 0;
+
 		drm_mode_probed_add(connector, mode);
 		return 1;
 	}