This eliminates the warning below as well

 | pipes.c: In function ‘open_pipe’:
 | pipes.c:252:6: error: variable ‘ret’ set but not used [-Werror=unused-but-set-variable]
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>