asus-nb-wmi.c: Rename x401u quirk to wapf4

The actual x401u does not use the so named x401u quirk but the x55u quirk.
All that the x401u quirk does it setting wapf to 4, so rename it to wapf4 to
stop the confusion.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>