msm: clock: Refactor clk_set_rate()

The refactor makes the code more readable and maintainable. Also, it avoids
sending out a clk_set_rate() trace point when rate change does not occur
due to an invalid argument.

Change-Id: I848301a2fc5ddc4080e75daaaf53163db2588736
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>