rtw88: no need to set registers for SDIO

There's no need to set SDIO related registers when powering up/down the chip.

Signed-off-by: Kevin Lo <kevlo@kevlo.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200515061153.GA15714@ns.kevlo.org