Fix typo.

From-SVN: r244781

gcc/ada/freeze.adb

@@ -8050,7 +8050,7 @@ package body Freeze is
       end if;
 
       --  Ensure that all anonymous access-to-subprogram types inherit the
-      --  covention of their related subprogram (RM 6.3.1 13.1/3). This is
+      --  convention of their related subprogram (RM 6.3.1 13.1/3). This is
       --  not done for a defaulted convention Ada because those types also
       --  default to Ada. Convention Protected must not be propagated when
       --  the subprogram is an entry because this would be illegal. The only