mmc: sdhci: Rename adma_desc to adma_table

In preparation for 64-bit ADMA, rename adma_desc to
adma_table.  That is because members will be added
for descriptor size and table size, so using adma_desc
(which is the table) is confusing.

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