MEMDISK: Fix register messup in EDD

MEMDISK: Fix register messup in EDD

Hello all,

I ran across a couple bugs in memdisk concerning hd images the other
day.  With the attached patch I've been able to successfully boot a
32MB gzipped hd image.  (I'll put the image up for a short while at
ftp://ftp.io.com/pub/usr/duanev/fdoshd.img.gz)

The pxelinux.cfg entry I'm using is:

    label fdos
        kernel memdisk
        append keeppxe initrd=fdoshd.img.gz

syslinux/memdisk is great, thanks Peter et. al.!

--
Duane Voth
duanev@io.com

Signed-off-by: H. Peter Anvin <hpa@zytor.com>