mmc: sdhci_am654: Update delay chain configuration

For speed modes where DLL is not enabled write to TXDLYCLK to enable
transmitter delay chain mode.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Link: https://lore.kernel.org/r/20200619125801.9530-6-faiz_abbas@ti.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>