ext4: add missing kfree() on error return path in add_new_gdb()

commit c49bafa3842751b8955a962859f42d307673d75d upstream.

We added some more error handling in b40971426a "ext4: add error
checking to calls to ext4_handle_dirty_metadata()".  But we need to
call kfree() as well to avoid a memory leak.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>