fbdev: fbcon: Destroy mutex on freeing struct fb_info

It's needed to destroy bl_curve_mutex on freeing struct fb_info since
the mutex is embedded in the structure and initialized when it's
allocated.
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Signed-off-by: Helge Deller <deller@gmx.de>

drivers/video/fbdev/core/fbsysfs.c

@@ -84,6 +84,10 @@ void framebuffer_release(struct fb_info *info)
 	if (WARN_ON(refcount_read(&info->count)))
 		return;
 
+#if IS_ENABLED(CONFIG_FB_BACKLIGHT)
+	mutex_destroy(&info->bl_curve_mutex);
+#endif
+
 	kfree(info->apertures);
 	kfree(info);
 }