drm/gma500: fix null pointer dereference in psb_intel_lvds_get_modes

In the Linux kernel, the following vulnerability has been resolved: 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.