ACPI: processor: idle: Fix NULL pointer dereference in hotplug path

ACPI: processor: idle: Fix NULL pointer dereference in hotplug path

A cpuidle_device might fail to register during boot, but the system can
continue to run. In such cases, acpi_processor_hotplug() can trigger
a NULL pointer dereference when accessing the per-cpu acpi_cpuidle_device.

So add NULL pointer check for the per-cpu acpi_cpuidle_device in
acpi_processor_hotplug.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Link: https://patch.msgid.link/20260403090253.998322-1-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>