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

For standard  requirement, I2C source
speed of 50MHz causes high power usage, hence
this patch change the clock rate to 19.2 MHz
to save power.

CRs-Fixed: 552956
Change-Id: Ifb17fb79062a390a19881d247a2ac0ca5cc55d80
Signed-off-by: Sana Venkat Raju <c_vsana@codeaurora.org>