ath5k: fix error handling in ath5k_hw_dma_stop

Review spotted a problem with the error handling in ath5k_hw_dma_stop:
a successful return from ath5k_hw_stop_tx_dma will be treated as
an error, so we always bail out of the loop after processing a single
active queue.  As a result, we may not actually stop some queues during
reset.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Bruno Randolf <br1@einfach.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Reviewed-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>