Fix zx_port_{wait,queue} packet count argument

In the near future zx_port_{wait,queue} will not accept a count of zero.
Change all callers to call these functions with a count of one.

Change-Id: I1a3fbcbb051c1da674fd6080685abd8c26067170
Reviewed-on: https://chromium-review.googlesource.com/1015481
Commit-Queue: Garret Kelly <gdk@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551415}

base/fuchsia/async_dispatcher.cc

@@ -119,7 +119,7 @@ zx_status_t AsyncDispatcher::DispatchOrWaitUntil(zx_time_t deadline) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
 
   zx_port_packet_t packet = {};
-  zx_status_t status = zx_port_wait(port_.get(), deadline, &packet, 0);
+  zx_status_t status = zx_port_wait(port_.get(), deadline, &packet, 1);
   if (status != ZX_OK)
     return status;