mmc: renesas_sdhi: remove always false condition

renesas_sdhi_probe() always sets host->dma as follows:

        host->dma               = dma_priv;

!host->dma is always false.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>