mmc: sdhci: Fix CMD line reset interfering with ongoing data transfer

CMD line reset during an ongoing data transfer can cause the data transfer
to hang.  Fix by delaying the reset until the data transfer is finished.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org # v4.8+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>