thermal: intel: hfi: Rename HFI_UPDATE_INTERVAL

The name of the constant HFI_UPDATE_INTERVAL is misleading. It is not a
periodic interval at which HFI updates are processed. It is the delay in
the processing of an HFI update after the arrival of an HFI interrupt.

Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>