ASoC: wcd9xxx: Add codec clock rate in device tree

-Wcd9xxx codec can run with different master clock
 rate. Codec needs to know the master clock rate
 at init to update default register values. Master
 clock rate is added to device tree.
-Remove use of static variable in codec I2C probe.

Change-Id: I6ba2821092e2f7e7814216ee49042845bcfdfe79
Signed-off-by: Venkat Sudhir <vsudhir@codeaurora.org>