Revert "devfreq: bwmon: Serialize update_devfreq with governor start/stop()"

The commit 'e42d9b00' causes a deadlock
as it introduces reverse lock ordering between df->lock and mon_lock.
Below is the sequence for the deadlock.

       gov_stop					update_bw_hwmon
mutex_lock(&df->lock)			mutex_lock(&node->mon_lock);
........					........
stop_monitor(df,true)			mutex_lock(&df->lock);
	mutex_lock(&node->mon_lock);		update_devfreq();
        ....
	mutex_unlock(&node->mon_lock);		mutex_unlock(&df->lock);
...						.........
mutex_unlock(&df->lock)			mutex_unlock(&node->mon_lock);

Hence revert this commit to fix the deadlock. This reverts commit
e42d9b00.

Change-Id: I1c4bd52ac462b4f1fdec4b494b6fb74e00fd72f8
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>