[U-Boot] efi_loader: Fix disk dp's for pre-DM/legacy devices

[Alexander Graf]

> This fixes an issue with OpenBSD's bootloader, and I think should also
> fix a similar issue with grub2 on legacy devices.  In the legacy case
> we were creating disk objects for the partitions, but not also the
> parent device.
> 
> Reported-by: Jonathan Gray <jsg at jsg.id.au>
> Signed-off-by: Rob Clark <robdclark at gmail.com>

Thanks, applied to efi-next

Alex