thinkpad-acpi: silence bogus complain during rmmod

Fix this bogus warning during module shutdown, when
backlight event reporting is enabled:

"thinkpad_acpi: required events 0x00018000 not enabled!"
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -2189,7 +2189,8 @@ static int hotkey_mask_set(u32 mask)
 		       fwmask, hotkey_acpi_mask);
 	}
 
-	hotkey_mask_warn_incomplete_mask();
+	if (tpacpi_lifecycle != TPACPI_LIFE_EXITING)
+		hotkey_mask_warn_incomplete_mask();
 
 	return rc;
 }