cpuctl_do_cpuid: explicitly use ecx=0 for cpuid call

... instead of whatever random value may happen to be in the register.
ecx is important to some cpuid leaves.

To do: extend cpuctl interface to provide for ecx value parameter.

MFC after:	5 days

sys/dev/cpuctl/cpuctl.c

@@ -204,7 +204,7 @@ cpuctl_do_cpuid(int cpu, cpuctl_cpuid_args_t *data, struct thread *td)
 	oldcpu = td->td_oncpu;
 	is_bound = cpu_sched_is_bound(td);
 	set_cpu(cpu, td);
-	do_cpuid(data->level, data->data);
+	cpuid_count(data->level, 0, data->data);
 	restore_cpu(oldcpu, is_bound, td);
 	return (0);
 }