[Ada] Small tweak in a couple of comments

[Pierre-Marie de Rodat]

This makes the comments use the same syntax as -gnatD/G for freeze nodes.

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

gcc/ada/

        * sem_ch12.adb (Freeze_Subprogram_Body): Add missing "freeze".
        (Install_Body): Likewise.
diff --git a/gcc/ada/sem_ch12.adb b/gcc/ada/sem_ch12.adb
--- a/gcc/ada/sem_ch12.adb
+++ b/gcc/ada/sem_ch12.adb
@@ -9106,7 +9106,7 @@ package body Sem_Ch12 is
          --  Handle the following case:
          --
          --    package Parent_Inst is new ...
-         --    Parent_Inst []
+         --    freeze Parent_Inst []
          --
          --    procedure P ...  --  this body freezes Parent_Inst
          --
@@ -9942,7 +9942,7 @@ package body Sem_Ch12 is
                --  Handle the following case:
 
                --    package Parent_Inst is new ...
-               --    Parent_Inst []
+               --    freeze Parent_Inst []
 
                --    procedure P ...  --  this body freezes Parent_Inst