wifi: rsi: Do not set MMC_PM_KEEP_POWER in shutdown

It makes no sense to set MMC_PM_KEEP_POWER in shutdown. The flag
indicates to the MMC subsystem to keep the slot powered on during
suspend, but in shutdown the slot should actually be powered off.
Drop this call.

Fixes: 063848c3

 ("rsi: sdio: Add WOWLAN support for S5 shutdown state")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230527222859.273768-1-marex@denx.de