vt: Add K_OFF return value to vt_ioctl KDGKBMODE

After adding support for K_OFF in KDSKBMODE, it was forgotten to
add support for returning it in KDGKBMODE.

Signed-off-by: Arthur Taylor <art@ified.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>