mmc: tegra: Force correct divider calculation on DDR50/52

Tegra SDHCI controllers require the SDHCI clock divider to be configured
to divide the clock by two in DDR50/52 modes. Incorrectly configured
clock divider results in corrupted data.

Prevent the possibility of incorrectly calculating the divider value due
to clock rate rounding or low parent clock frequency by not assigning
host->max_clk to clk_get_rate() on tegra_sdhci_set_clock().

See the comments for further details.

Fixes: a8e326a9 ("mmc: tegra: implement module external clock change")
Signed-off-by: Aapo Vienamo <avienamo@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>