tty: fix vt_compat_ioctl

Call compat_unimap_ioctl, not do_unimap_ioctl.

This was broken by commit e9216651.

The compat_unimap_ioctl was originally called do_unimap_ioctl in
fs/compat_ioctl.h which got moved to drivers/char/vt_ioctl.c.
In that patch, the caller was not updated and consequently called
the native handler.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>