mmc: rtsx_usb_sdmmc: Add 74 clocks in poweron flow

To conform with SD spec definition, that the host must provide at least 74
clocks before issuing first command, let's add these clock cycles at
MMC_POWER_UP.

Signed-off-by: Ricky Wu <ricky_wu@realtek.com>
Link: https://lore.kernel.org/r/20250616064956.1846258-1-ricky_wu@realtek.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>