WMI: properly cleanup devices to avoid crashes

We need to remove devices that we destroy from the list, otherwise
we'll crash if there are more than one "_WDG" methods in DSDT.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=32052

Tested-by: Ilya Tumaykin <librarian_rus@yahoo.com>
Cc: stable@kernel.org
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Acked-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Signed-off-by: Matthew Garrett <mjg@redhat.com>