wifi: rsi: rsi_91x_debugfs: Remove unnecessary (void*) conversions

No need cast (void*) to (struct rsi_91x_sdiodev *).

Signed-off-by: Wu Yunchuan <yunchuan@nfschina.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230803073455.3666306-1-yunchuan@nfschina.com