tty: Fix mistyping of /dev/tty

/dev/tty stands for current terminal which we don't yet
implemented a support for.

This is a bugfix for upcoming stable version, the proper
support of /dev/tty is gonna be implemented separately.

Reported-by: Saied Kazemi <saied@google.com>
CC: Andrew Vagin <avagin@parallels.com>
CC: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>