clk: qcom: Move set_rate ops check after checking rate

There are some clk_ops where we don't want to support setting a rate,
because its rate will be pre-configured. However, we still want
clk_set_rate() to succeed if it's called with same rate as current
rate.

Instead of requiring clk_ops put a stub set_rate ops, move this
functionality into core clock framework.

Change-Id: I40b99b2805fae526a44eb2556802819a80d29e75
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>