msm: clock-copper: Initialize ocmemnoc clock rate in post_init

Set the rate of the OCMEM NoC clock source in post_init,
since the branches off of this source may be enabled
before the bus driver is ready to set a rate on this NoC.

Change-Id: I55322037924babe946c3cd54845bb6cca6100eb1
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>