staging: r8188eu: Use completions for signaling start / end kthread

staging: r8188eu: Use completions for signaling start / end kthread

rtw_cmd_thread() "up(s)" a semaphore twice, first to notify callers when
its execution is started and then to notify when it is about to end.

It makes the same semaphore go "up" twice in the same thread. This
construct makes Smatch to warn of duplicate "up(s)".

This thread uses interruptible semaphores where instead completions are
more suitable. For this purpose it calls an helper (_rtw_down_sema())
that returns values that are never checked. It may lead to bugs.

To address the above-mentioned issues, use two completions variables
instead of semaphores. Use the uninterruptible versions of
wake_for_completion*() because the interruptible / killable versions are
not necessary.

Tested with "ASUSTek Computer, Inc. Realtek 8188EUS [USB-N10 Nano]".

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20211018162006.5527-2-fmdefrancesco@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>