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>