rockchip: dwmmc: use max-frequency when OF_PLATDATA enabled

Since the 'clock-freq-min-max' is deprecated, we use max-frequency for
all rockchip SoC dwmmc controller.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>