Always return something.

This commit was SVN r26099.

ompi/datatype/ompi_datatype.h

@@ -290,6 +290,7 @@ ompi_datatype_copy_content_same_ddt( const ompi_datatype_t* type, size_t count,
         if( 0 != rc ) return rc;
         count -= (size_t)length;
     }
+    return 0;
 }
 
 OMPI_DECLSPEC const ompi_datatype_t* ompi_datatype_match_size( int size, uint16_t datakind, uint16_t datalang );