staging: bcm2708_vchiq: fix return value check in vchiq_init_state()

In case of error, the function kthread_create() returns ERR_PTR() and
never returns NULL. The NULL test in the return value check should be
replaced with IS_ERR().

Signed-off-by: Wei Yongjun <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c

···
 		(void *)state,
 		threadname);
 
-	if (state->slot_handler_thread == NULL) {
+	if (IS_ERR(state->slot_handler_thread)) {
 		vchiq_loud_error_header();
 		vchiq_loud_error("couldn't create thread %s", threadname);
 		vchiq_loud_error_footer();
···
 	state->recycle_thread = kthread_create(&recycle_func,
 		(void *)state,
 		threadname);
-	if (state->recycle_thread == NULL) {
+	if (IS_ERR(state->recycle_thread)) {
 		vchiq_loud_error_header();
 		vchiq_loud_error("couldn't create thread %s", threadname);
 		vchiq_loud_error_footer();
···
 	state->sync_thread = kthread_create(&sync_func,
 		(void *)state,
 		threadname);
-	if (state->sync_thread == NULL) {
+	if (IS_ERR(state->sync_thread)) {
 		vchiq_loud_error_header();
 		vchiq_loud_error("couldn't create thread %s", threadname);
 		vchiq_loud_error_footer();