ext4: destroy ext4_es_cachep on module unload

Without this, module can't be reloaded.

[  500.521980] kmem_cache_sanity_check (ext4_extent_status): Cache name already exists.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org  # v3.8+

fs/ext4/super.c

@@ -5481,6 +5481,7 @@ static void __exit ext4_exit_fs(void)
 	kset_unregister(ext4_kset);
 	ext4_exit_system_zone();
 	ext4_exit_pageio();
+	ext4_exit_es();
 }
 
 MODULE_AUTHOR("Remy Card, Stephen Tweedie, Andrew Morton, Andreas Dilger, Theodore Ts'o and others");