mmc: mmci: Get rid of dead code in mmci_dma_setup

DMA configuration has been removed from function mmci_dma_setup but the
local mask variable was not removed. This remains unused hence remove
it from the function and operations on it

Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>