mmc: dw_mmc: init desc in dw_mci_idmac_init

Set 0 to des1 in 32bit case.
Otherwise the random value of des1 will be used in
dw_mci_translate_sglist: IDMAC_SET_BUFFER1_SIZE(desc, length)

Signed-off-by: Fei Wang <w.f@huawei.com>
Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>