mmc: mxs-mmc: Fix additional cycles after transmission stop

According to the code the intention is to append 8 SCK cycles
instead of 4 at end of a MMC_STOP_TRANSMISSION command. But this
will never happened because it's an AC command not an ADTC command.
So fix this by moving the statement into the right function.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Fixes: e4243f13

 (mmc: mxs-mmc: add mmc host driver for i.MX23/28)
Cc: <stable@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>