msm: clock-local2: Move lock from rcg_clk_set_rate to lower level ops

The local_clock_reg_lock is used to protect registers accesses. Move
the acquiring and releasing of this lock from rcg_clk_set_rate to
set_rate_mnd and set_rate_hid to allow overriding of the RCG set rate
op with ops that dont require the lock.

Change-Id: I2d04b71f12f91d2cd5ef14f05a908558ed149488
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>