MINOR: map/pattern: The sample parser is stored in the pattern

We cannot separe the pattern and the value. Now, the patern known the
value and the pattern is able to parsehis associated sample staroage.
diff --git a/include/types/pattern.h b/include/types/pattern.h
index 7b9f8fd..72022e3 100644
--- a/include/types/pattern.h
+++ b/include/types/pattern.h
@@ -155,6 +155,7 @@
  */
 struct pattern_expr {
 	int (*parse)(const char *text, struct pattern *pattern, char **err);
+	int (*parse_smp)(const char *text, struct sample_storage *smp);
 	int (*index)(struct pattern_expr *, struct pattern *, char **);
 	void (*delete)(struct pattern_expr *, struct pattern *);
 	struct sample_storage **(*find_smp)(struct pattern_expr *, struct pattern *);