Fix a JSON CPU information bug.

When using the JSON monitor, qemuMonitorJSONExtractCPUInfo
was returning 0 on success.  Unfortunately, higher levels of
the cpuinfo code expect that it returns the number of CPUs
it found on success.  This one-line patch fixes it so that
it returns the correct number.  This makes "virsh vcpuinfo <domain>"
work when using the JSON monitor.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

src/qemu/qemu_monitor_json.c

@@ -648,7 +648,7 @@ qemuMonitorJSONExtractCPUInfo(virJSONValuePtr reply,
 
     *pids = threads;
     threads = NULL;
-    ret = 0;
+    ret = ncpus;
 
 cleanup:
     VIR_FREE(threads);