ARM: dts: msm: i2c: change clock rate to 19.2 MHz

For standard  requirement, I2C source
speed of 24MHz, hence
this patch change the clock rate to 19.2 MHz
to save power.

https://github.com/xboxfanj/android_kernel_htc_msm8974/commit/fe7fc6b1e5f983f8c27943e82141af9b22eddcd7#diff-b67083b4967a87b3eb2971190d76f521R861