kernel: change i2c1 frequency from 400K to 100K

Some I2C devices can only operate at a frequency of 100KHz

build/boards/cv180x/cv1800b_milkv_duo_sd/dts_riscv/cv1800b_milkv_duo_sd.dts

@@ -20,6 +20,11 @@
 	status = "okay";
 };
 
+&i2c1 {
+       status = "okay";
+       clock-frequency = <100000>;
+};
+
 / {
 
 };