staging: wfx: fix __wfx_flush() when drop == false

staging: wfx: fix __wfx_flush() when drop == false

wfx_tx_queues_clear() only clear not yet sent requests. So, it always
necessary to wait for tx_queue_stats.wait_link_id_empty whatever the
value of "drop" argument.

In add, it is not necessary to return with tx queue locked since all
calls to __wfx_flush() unlock the tx queue just after the call to
__wfx_tx_flush().

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-20-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>