ada: Small tweak to latest change

Unlike RTE, RTU_Entity alone does not cause the unit to be loaded.

gcc/ada/ChangeLog:

	* exp_ch7.adb (Shift_Address_For_Descriptor): Add dummy variable
	to make sure that System_Storage_Elements is loaded.
diff --git a/gcc/ada/exp_ch7.adb b/gcc/ada/exp_ch7.adb
index 9abdcc1..4d2b834 100644
--- a/gcc/ada/exp_ch7.adb
+++ b/gcc/ada/exp_ch7.adb
@@ -8868,7 +8868,9 @@
       Typ    : Entity_Id;
       Op_Nam : Name_Id) return Node_Id
    is
-      Loc : constant Source_Ptr := Sloc (Addr);
+      Loc   : constant Source_Ptr := Sloc (Addr);
+      Dummy : constant Entity_Id  := RTE (RE_Storage_Offset);
+      --  Make sure System_Storage_Elements is loaded for RTU_Entity
 
    begin
       --  Generate: