staging: w35und: Add locking problems to TODO list

The w35und uses atomics such as "ThreadCount" and "FireCount" to emulate
locking in the TX paths, for example. Document this bug in the TODO list.

Cc: Lars Lindley <lindley@coyote.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Ruslan Pisarev <ruslan@rpisarev.org.ua>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>