[ticket/13010] Specifiy correct clean_row() call in phpbb_get_avatar docblock

PHPBB3-13010
Merge pull request #2907 from marc1706/ticket/13010

[ticket/13010] Specifiy correct clean_row() call in phpbb_get_avatar docblock

* marc1706/ticket/13010:
  [ticket/13010] Specifiy correct clean_row() call in phpbb_get_avatar docblock