ACPI: thinkpad-acpi: clean up hotkey_notify()

Clean up the hotkey_notify() handler, which handles the HKEY notifications
from the ACPI firmware.  It was getting too long and deep.

No functional changes.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>