Name, phys and uniq are quite often constant strings in moules implementing
particular input device. If a module unregisters input device and then gets
unloaded, the device could still be present in memory (pinned via sysfs),
but aforementioned members would point to some random memory. Set them all
to NULL when unregistering so sysfs handlers won't try dereferencing them.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>