MINOR: pattern: make the pattern matching function return a pointer to the matched element

This feature will be used by the CLI to look up keys.
diff --git a/src/map.c b/src/map.c
index a13c5b7..b1fa7f6 100644
--- a/src/map.c
+++ b/src/map.c
@@ -467,7 +467,7 @@
 	desc = arg_p[0].data.map;
 
 	/* Execute the match function. */
-	ret = pattern_exec_match(desc->pat, smp, &sample);
+	ret = pattern_exec_match(desc->pat, smp, &sample, NULL, NULL);
 	if (ret != PAT_MATCH) {
 		if (!desc->def)
 			return 0;