staging: rtl8723bs: change semaphores to completions

This driver uses many semaphores, most of them are equivalent to
completions. The other copies of this driver got moved over to
completions a while ago, so do the same here.

In this usage scenario, the two are equivalent, so the behavior
should not change.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>