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
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 143cfd6113)
Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>

target/linux/ramips/dts/mt7620a.dtsi

@@ -522,7 +522,7 @@
 		reg = <0x10130000 0x4000>;
 
 		bus-width = <4>;
-		max-frequency = <24000000>;
+		max-frequency = <48000000>;
 		cap-mmc-highspeed;
 		cap-sd-highspeed;
 		disable-wp;

target/linux/ramips/dts/mt7621.dtsi

@@ -347,7 +347,7 @@
 		reg = <0x1e130000 0x4000>;
 
 		bus-width = <4>;
-		max-frequency = <48000000>;
+		max-frequency = <50000000>;
 		cap-mmc-highspeed;
 		cap-sd-highspeed;
 		disable-wp;

target/linux/ramips/dts/mt7628an.dtsi

@@ -376,7 +376,7 @@
 		reg = <0x10130000 0x4000>;
 
 		bus-width = <4>;
-		max-frequency = <24000000>;
+		max-frequency = <48000000>;
 		cap-mmc-highspeed;
 		cap-sd-highspeed;
 		disable-wp;