mmc: mmci: define get_dctrl_cfg for legacy variant

This patch defines get_dctrl_cfg callback for legacy variants
whatever DMA_ENGINE configuration.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
[Ulf: Fixed a build error]
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>