mmc: mtk-sd: fix hang when data read quickly

For CMD21 tuning data, the 128/64 bytes data may coming in very
short time, before msdc_start_data(), the read data has already
come, in this case, clear MSDC_INT will cause the interrupt disappear
and lead to the thread hang.

the solution is just clear all interrupts before command was sent.

Signed-off-by: mingming lee <mingming.lee@mediatek.com>