mmc: tegra: fix ddr signaling for non-ddr modes

ddr_signaling is set to true for DDR50 and DDR52 modes but is
not set back to false for other modes. This programs incorrect
host clock when mode change happens from DDR52/DDR50 to other
SDR or HS modes like incase of mmc_retune where it switches
from HS400 to HS DDR and then from HS DDR to HS mode and then
to HS200.

This patch fixes the ddr_signaling to set properly for non DDR
modes.

Tested-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Cc: stable@vger.kernel.org # v4.20 +
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>