[Ada] Fix inconsistent parameter of SPARK_Msg_NE

[Pierre-Marie de Rodat]

All calls to SPARK_Msg_NE except one were taking an entity as its second
parameter; this patch does the same for one call that took an
identifier.

Code cleanup only; behaviour is unaffected, because both entity and
identifier works in the same when given to SPARK_Msg_NE routine.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * sem_prag.adb (Analyze_Global_Item): Call SPARK_Msg_NE with the
        entity, not with its identifier.
diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb
--- a/gcc/ada/sem_prag.adb
+++ b/gcc/ada/sem_prag.adb
@@ -2385,7 +2385,7 @@ package body Sem_Prag is
 
                   if Ekind (Item_Id) in Named_Kind then
                      SPARK_Msg_NE
-                       ("\named number & is not an object", Item, Item);
+                       ("\named number & is not an object", Item, Item_Id);
                   end if;
 
                   return;