[U-Boot] efi_loader: fix bug in efi_get_memory_map

[Alexander Graf]

> When booting shim -> fallback -> shim -> grub -> linux the memory map is
> a bit larger than the size linux passes in on the first call.  But in
> the EFI_BUFFER_TOO_SMALL case we were not passing back the updated size
> to linux so it would loop forever.
> 
> Signed-off-by: Rob Clark <robdclark at gmail.com>

Thanks, applied to efi-next

Alex