[Ada] Revert mistaken negation related to references to labels

[Pierre-Marie de Rodat]

Commit titled "Update handling of assigned value/unreferenced warnings"
added a comment "... *unless* this is an actual parameter" and at the
same time removed a "not" operator from the corresponding condition.
This is now reverted to match both the previous code and the current
comment.

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

gcc/ada/

        * sem_ch8.adb (Find_Direct_Name): Fix code to match the comment.
diff --git a/gcc/ada/sem_ch8.adb b/gcc/ada/sem_ch8.adb
--- a/gcc/ada/sem_ch8.adb
+++ b/gcc/ada/sem_ch8.adb
@@ -6047,9 +6047,9 @@ package body Sem_Ch8 is
 
                begin
                   --  Generate reference unless this is an actual parameter
-                  --  (see comment below)
+                  --  (see comment below).
 
-                  if Reference_OK and then Is_Actual_Parameter then
+                  if Reference_OK and then not Is_Actual_Parameter then
                      Generate_Reference (E, N);
                      Set_Referenced (E, R);
                   end if;