ath6kl: fix control-message timeout

USB control-message timeouts are specified in milliseconds and should
specifically not vary with CONFIG_HZ.

Fixes: 241b128b

 ("ath6kl: add back beginnings of USB support")
Cc: stable@vger.kernel.org      # 3.4
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211025120522.6045-3-johan@kernel.org