Fix af_NA wrong separator inheritance, use en_NA instead of af_ZA (en_ZA)

It didn't matter originally, but en_ZA separators changed with

    commit 5c10c448
    CommitDate: Mon Sep 3 13:38:13 2018 +0200

        tdf#119613 [*-ZA] decimal separator is comma, group separator is space

and

    commit 464154aa
    CommitDate: Mon Sep 3 13:38:23 2018 +0200

        Related: tdf#119613 inherit af_ZA separators from identical en_ZA

so the separators didn't match the formats inherited from en_NA
anymore.

Change-Id: Iccf951b27b5575706e0f6bae12b5df4b53e335ac

i18npool/source/localedata/data/af_NA.xml

@@ -28,7 +28,7 @@
       <DefaultName>Namibia</DefaultName>
     </Country>
   </LC_INFO>
-  <LC_CTYPE ref="af_ZA"/>
+  <LC_CTYPE ref="en_NA"/>
   <LC_FORMAT ref="en_NA" replaceTo="[$$-8036]"/>
   <LC_COLLATION ref="en_US"/>
   <LC_SEARCH ref="en_US"/>