video: of: display_timing: double free on error

The display_timings_release() function frees "disp" and we free it
again on the next line.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/of_display_timing.c

@@ -236,6 +236,7 @@ struct display_timings *of_get_display_timings(struct device_node *np)
 	if (native_mode)
 		of_node_put(native_mode);
 	display_timings_release(disp);
+	disp = NULL;
 entryfail:
 	kfree(disp);
 dispfail: