mmc: sdhci: Rename two ADMA-related functions for consistency

Rename sdhci_set_adma_desc to sdhci_adma_write_desc and
sdhci_show_adma_error to sdhci_adma_show_error so that
all ADMA functions start with sdhci_adma_.

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