mmc: mmc: Fix incorrect use of driver strength switching HS200 and HS400

mmc: mmc: Fix incorrect use of driver strength switching HS200 and HS400

Commit cc4f414c885c ("mmc: mmc: Add driver strength selection")
added driver strength selection for eMMC HS200 and HS400 modes.
That patch also set the driver stength when transitioning through
High Speed mode to HS200/HS400, but driver strength is not defined
for High Speed mode.  While the JEDEC specification is not clear
on this point it has been observed to cause problems for some eMMC,
and removing the driver strength setting in this case makes it
consistent with the normal use of High Speed mode.

Signed-off-by: Wenkai Du <wenkai.du@intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>