efi_loader: helper function to add EFI object to list

To avoid duplicate coding provide a helper function that
initializes an EFI object and adds it to the EFI object
list.

efi_exit() is the only place where we dereference a handle
to obtain a protocol interface. Add a comment to the function.

Suggested-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_loader/efi_disk.c b/lib/efi_loader/efi_disk.c
index af8db40..68ba2cf 100644
--- a/lib/efi_loader/efi_disk.c
+++ b/lib/efi_loader/efi_disk.c
@@ -224,13 +224,11 @@
 		goto out_of_memory;
 
 	/* Hook up to the device list */
-	INIT_LIST_HEAD(&diskobj->parent.protocols);
-	list_add_tail(&diskobj->parent.link, &efi_obj_list);
+	efi_add_handle(&diskobj->parent);
 
 	/* Fill in object data */
 	diskobj->dp = efi_dp_from_part(desc, part);
 	diskobj->part = part;
-	diskobj->parent.handle = diskobj;
 	ret = efi_add_protocol(diskobj->parent.handle, &efi_block_io_guid,
 			       &diskobj->ops);
 	if (ret != EFI_SUCCESS)