mmc: sdhci: fix __sdhci_adma_write_desc

If hosts provides ops->adma_write_desc, we should not fall back to the
general sdhci_adma_write_desc().

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>