ramips: dts: increase maximum MMC clock frequency

ramips: dts: increase maximum MMC clock frequency

The High-Speed SD mode stability issue should have been fixed.
Increase the MMC max-frequency to improve the IO speed. We can
still use the sysfs to limit the clock frequency, e.g.

root@OpenWrt:~# echo 25000000 > /sys/kernel/debug/mmc0/clock

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/18896
(cherry picked from commit 143cfd6113231c61f38d1b9f5a0ea9ce3cc986c5)
Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>
Link: https://github.com/openwrt/openwrt/pull/20258
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>