mmc: mediatek: correct the implementation of msdc_card_busy

msdc_card_busy only need check if the data0 is low.
In sdio data1 irq mode, data1 may be low because of interruption.

Signed-off-by: Yong Mao <yong.mao@mediatek.com>
Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>