efi_loader: Fix loaded_image handle passing from EL3

When running in EL3 mode on AArch64, we have to first drop to EL2
to execute a UEFI payload. When dropping down, the arguments to
the entry point have to stay identical to the ones for normal entry
though.

In commit ea54ad59 ("efi_loader: pass handle of loaded image")
we incorrectly changed that logic and had the el3 entry path diverge.
Fix it up by syncing it back to what it's supposed to be.

Fixes: ea54ad59 ("efi_loader: pass handle of loaded image")
Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>