workqueue: avoid using deprecated functions

The network merge brought in a few users of functions that got
deprecated by the workqueue cleanups: the 'system_nrt_wq' is now the
same as the regular system_wq, since all workqueues are now non-
reentrant.

Similarly, remove one use of flush_work_sync() - the regular
flush_work() has become synchronous, and the "_sync()" version is thus
deprecated as being superfluous.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/net/ieee802154/mrf24j40.c

@@ -718,7 +718,7 @@ static int __devexit mrf24j40_remove(struct spi_device *spi)
 	dev_dbg(printdev(devrec), "remove\n");
 
 	free_irq(spi->irq, devrec);
-	flush_work_sync(&devrec->irqwork); /* TODO: Is this the right call? */
+	flush_work(&devrec->irqwork); /* TODO: Is this the right call? */
 	ieee802154_unregister_device(devrec->dev);
 	ieee802154_free_device(devrec->dev);
 	/* TODO: Will ieee802154_free_device() wait until ->xmit() is