gbl: efi: src: android_boot.rs: let fdt_bytes not mutable

When compiling without EFI FDT, we have the following error:
    let fdt_origin = Fdt::new(fdt_bytes)?;
                              --------- value moved here
 ...
    let mut fdt = Fdt::new_from_init(&mut load[..], fdt_bytes)?;
                                                    ^^^^^^^^^ value borrowed
                                                             here after move

Let fdt_bytes non-mutable solves this problem.

Change-Id: I86b973ce6a0ae3563e87458575e037004f70ea15
Signed-off-by: Ying-Chun Liu (PaulLiu) <liupa@google.com>