CIFS: fix memory leak and remove dead code

also fixes error code in smb311_posix_mkdir() (where
the error assignment needs to go before the goto)
a typo that Dan Carpenter and Paulo and Gustavo
pointed out.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>