wifi: ath5k: remove unnecessary (void*) conversions

No need cast (void *) to (struct ath5k_hw *).

Signed-off-by: Wu Yunchuan <yunchuan@nfschina.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230919044959.523576-1-yunchuan@nfschina.com