i2c: lpi2c: Avoid calling clk_get_rate during transfer

In the Linux kernel, the following vulnerability has been resolved:

i2c: lpi2c: Avoid calling clk_get_rate during transfer

Instead of repeatedly calling clk_get_rate for each transfer, lock

the clock rate and cache the value.

A deadlock has been observed while adding tlv320aic32x4 audio codec to

the system. When this clock provider adds its clock, the clk mutex is

locked already, it needs to access i2c, which in return needs the mutex

for clk_get_rate as well.