mmc: tegra: Remove tegra_sdhci_writew() from tegra210_sdhci_ops

tegra_sdhci_writew() defers the write to SDHCI_TRANSFER_MODE until
SDHCI_COMMAND is written. This is not necessary on Tegra210 and Tegra186
and it breaks read-modify-write operations on SDHCI_TRANSFER_MODE
because writes to SDHCI_TRANSFER_MODE aren't visible until SDHCI_COMMAND
has been written to. This results in tuning failures on Tegra210.

Signed-off-by: Aapo Vienamo <avienamo@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>