rockchip: rk3288: dtsi use max-frequency for mmc node

Since the 'clock-freq-min-max' is deprecated, we use max-frequency.

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>