hwmon: (hp-wmi-sensors) Check if WMI event data exists

In the Linux kernel, the following vulnerability has been resolved:

hwmon: (hp-wmi-sensors) Check if WMI event data exists

The BIOS can choose to return no event data in response to a WMI event, so the ACPI object passed to the WMI notify handler can be NULL.

Check for such a situation and ignore the event in such a case.