wifi: rsi: rsi_91x_usb: Remove unnecessary (void*) conversions

No need cast (void*) to (struct rsi_91x_usbdev *).

Signed-off-by: Wu Yunchuan <yunchuan@nfschina.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230803073558.3666936-1-yunchuan@nfschina.com