at86rf230: remove hrtimer on 1 usec delay

According Documentation/timers/timers-howto.txt the usually case for
setting up a hrtimer takes > ~10us. So we should use udelay in this
case so we are sure that the state change was done, before doing the
state change assert.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/net/ieee802154/at86rf230.c

@@ -545,7 +545,9 @@ at86rf230_async_state_delay(void *context)
 	}
 
 	/* Default delay is 1us in the most cases */
-	tim = ktime_set(0, NSEC_PER_USEC);
+	udelay(1);
+	at86rf230_async_state_timer(&ctx->timer);
+	return;
 
 change:
 	hrtimer_start(&ctx->timer, tim, HRTIMER_MODE_REL);