staging: wfx: remove false-positive WARN()

staging: wfx: remove false-positive WARN()

The function wfx_tx_flush() wait for there is no more queued frames in
hardware queue. Then, for the sanity, it checks that there is no more
pending frame on any AC queue.

However, there is a race here. It may happens that hardware queues are
empty, but the counters of the AC queues are not yet updated. So, it may
produce false-positive warning.

The easiest way to solve the problem is just to remove the sanity check.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200515083325.378539-18-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>