staging: rtl8723au: Use workqueue to handle interrupt complete processing

Split the old work handler into a workqueue for processing
usb_read_interrupt_complete() events that require more than ust
clearing the event, and leave the old handler to just handle event
clearing.

This means we can get rid of the hacks with magic pointers to
determine what actions needs to be taken in the work handler, and
as an extra bonus obsoletes the bizarre cbuf code.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>