tracing: Have the historgram use the result of str_has_prefix() for len of prefix

As str_has_prefix() returns the length on match, we can use that for the
updating of the string pointer instead of recalculating the prefix size.

Cc: Tom Zanussi  <zanussi@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -4342,12 +4342,13 @@ static int parse_actions(struct hist_trigger_data *hist_data)
 	unsigned int i;
 	int ret = 0;
 	char *str;
+	int len;
 
 	for (i = 0; i < hist_data->attrs->n_actions; i++) {
 		str = hist_data->attrs->action_str[i];
 
-		if (str_has_prefix(str, "onmatch(")) {
-			char *action_str = str + sizeof("onmatch(") - 1;
+		if ((len = str_has_prefix(str, "onmatch("))) {
+			char *action_str = str + len;
 
 			data = onmatch_parse(tr, action_str);
 			if (IS_ERR(data)) {
@@ -4355,8 +4356,8 @@ static int parse_actions(struct hist_trigger_data *hist_data)
 				break;
 			}
 			data->fn = action_trace;
-		} else if (str_has_prefix(str, "onmax(")) {
-			char *action_str = str + sizeof("onmax(") - 1;
+		} else if ((len = str_has_prefix(str, "onmax("))) {
+			char *action_str = str + len;
 
 			data = onmax_parse(action_str);
 			if (IS_ERR(data)) {