ref-filter: use non-const ref_format in *_atom_parser()

Use non-const ref_format in *_atom_parser(), which can help us
modify the members of ref_format in *_atom_parser().

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: ZheNing Hu <adlternative@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/ref-filter.h b/ref-filter.h
index baf72a7..74fb423 100644
--- a/ref-filter.h
+++ b/ref-filter.h
@@ -116,7 +116,7 @@ void ref_array_sort(struct ref_sorting *sort, struct ref_array *array);
 void ref_sorting_set_sort_flags_all(struct ref_sorting *sorting, unsigned int mask, int on);
 /*  Based on the given format and quote_style, fill the strbuf */
 int format_ref_array_item(struct ref_array_item *info,
-			  const struct ref_format *format,
+			  struct ref_format *format,
 			  struct strbuf *final_buf,
 			  struct strbuf *error_buf);
 /*  Parse a single sort specifier and add it to the list */
@@ -137,7 +137,7 @@ void setup_ref_filter_porcelain_msg(void);
  * name must be a fully qualified refname.
  */
 void pretty_print_ref(const char *name, const struct object_id *oid,
-		      const struct ref_format *format);
+		      struct ref_format *format);
 
 /*
  * Push a single ref onto the array; this can be used to construct your own