[pcbios] Always show INT 15,88 result under DEBUG=memmap

Always call INT 15,88 even if we don't use the result.  This allows
DEBUG=memmap to show the complete result set returned by all of the
INT 15 memory-map calls.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>