We should zero out the password before we free it.

Fixes: 3d6cacbb5310 ("cifs: Add DFS cache routines")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>
Reviewed-by: NPaulo Alcantara <palcantara@suse.de>