Added "const" to new data for handler::update_row()

This was done to make it clear that a update_row() should not change the
row.
This was not done for handler::write_row() as this function still needs
to update auto_increment values in the row. This should at some point
be moved to handler::ha_write_row() after which write_row can also have
const arguments.

storage/perfschema/table_setup_objects.cc

@@ -265,7 +265,7 @@ int table_setup_objects::read_row_values(TABLE *table,
 
 int table_setup_objects::update_row_values(TABLE *table,
                                            const unsigned char *,
-                                           unsigned char *,
+                                           const unsigned char *,
                                            Field **fields)
 {
   int result;