Clarify intention between comparison to zero and the shift operation

Building with (GNU Tools for Arm Embedded Processors 7-2017-q4-major) 7.2.1 20170904 gives this warning

../events/equeue/equeue.c: In function 'equeue_incid':
../events/equeue/equeue.c:40:17: warning: '<<' in boolean context, did you mean '<' ? [-Wint-in-bool-context]
     if (!(e->id << q->npw2)) {

equeue.c

@@ -26,7 +26,7 @@ static inline int equeue_clampdiff(unsigned a, unsigned b) {
 // Increment the unique id in an event, hiding the event from cancel
 static inline void equeue_incid(equeue_t *q, struct equeue_event *e) {
     e->id += 1;
-    if (!(e->id << q->npw2)) {
+    if (0 == (e->id << q->npw2)) {
         e->id = 1;
     }
 }