msm-core: Fix race with userspace updating power numbers

When the user space application updates the existing leakage values, the
existing structures are freed and updated. If the polling worker thread is
executed at the same time, the worker thread could end up accessing memory
locations that were freed earlier.

Fix by using critical sections around free/update of the data structures.

Change-Id: I611585842c420653c925f83959dac9710b50ee2b
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>