tracing: is_legal_op() can return boolean

Make is_legal_op() return bool to improve readability due to this particular
function only using either one or zero as its return value.

No functional change.

Link: http://lkml.kernel.org/r/1443537816-5788-8-git-send-email-bywxiaobai@163.comSigned-off-by: Yaowei Bai <bywxiaobai@163.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_events_filter.c

@@ -973,15 +973,15 @@ static bool is_string_field(struct ftrace_event_field *field)
 	       field->filter_type == FILTER_PTR_STRING;
 }
 
-static int is_legal_op(struct ftrace_event_field *field, int op)
+static bool is_legal_op(struct ftrace_event_field *field, int op)
 {
 	if (is_string_field(field) &&
 	    (op != OP_EQ && op != OP_NE && op != OP_GLOB))
-		return 0;
+		return false;
 	if (!is_string_field(field) && op == OP_GLOB)
-		return 0;
+		return false;
 
-	return 1;
+	return true;
 }
 
 static filter_pred_fn_t select_comparison_fn(int op, int field_size,