mmc: mediatek: fix incorrect register setting of hs400_cmd_int_delay

to set cmd internal delay, need set PAD_TUNE register but not PAD_CMD_TUNE
register.

Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
Fixes: 1ede5cb8 ("mmc: mediatek: Use data tune for CMD line tune")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>