mmc: jz4740: Use dma_request_chan()

Replace dma_request_channel() with dma_request_chan(),
which also supports probing from the devicetree.

Tested-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.co.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>