efi_memory: return MapKey

efi_get_memory_map should set a defined value for map_key.

We later can introduce the test against this value in
efi_exit_boot_services as required by the UEFI standard.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
index c56653f..f59e3ea 100644
--- a/lib/efi_loader/efi_memory.c
+++ b/lib/efi_loader/efi_memory.c
@@ -431,6 +431,8 @@
 		}
 	}
 
+	*map_key = 0;
+
 	return EFI_SUCCESS;
 }