driver-core: cpu: fix kobject warning when hotplugging a cpu

Due to the sysdev conversion to struct device, the cpu objects get
reused when adding a cpu after offlining it, which causes a big warning
that the kobject portion is not properly initialized.

So clear out the object before we register it again, so all is quiet.
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/cpu.c

@@ -240,6 +240,7 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
 	int error;
 
 	cpu->node_id = cpu_to_node(num);
+	memset(&cpu->dev, 0x00, sizeof(struct device));
 	cpu->dev.id = num;
 	cpu->dev.bus = &cpu_subsys;
 	cpu->dev.release = cpu_device_release;