vt: NULL dereference in vt_do_kdsk_ioctl()

We forgot to set the "key_map" variable here, so it's still NULL.  This
was introduced recently in 079c9534

 "vt:tackle kbd_table".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>