Remove superfluous "," introduced in [17328]

configure.ac

@@ -3088,7 +3088,7 @@ then
         VLC_ADD_CPPFLAGS([a52tofloat32],[${CPPFLAGS_test}])
       ],[
         AC_MSG_ERROR([Could not find liba52 on your system: you may get it from http://liba52.sf.net/. Alternatively you can use --disable-a52 to disable the a52 plugin.])
-        ]),
+        ])
     ],[
       AC_MSG_ERROR([Could not find liba52 on your system: you may get it from http://liba52.sf.net/. Alternatively you can use --disable-a52 to disable the a52 plugin.])
     ])