mmc: dw_mmc: rockchip: Fix modalias to make module auto-loading work

Make the modalias match driver name, this is required to make module
auto-loading work.

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
CC: Doug Anderson <dianders@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>