mmc: sh_mmcif: Fix DMA slave address configuration

Commit e5a233cb ("mmc: sh_mmcif:
Factorize DMA channel request and configuration code") incorrectly
set the destination address for both slave channels instead of setting
the source address for the receive channel. Fix that.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>