msm: mdss: rotator: turn off rotator clock in wq release

Commit 496e09e6 ("msm:
mdss: ensure rotator clocks on for entire rotator
session") moves rotator clock handling from workqueue
to session management. However, close_session will
not turn off the clock if there is a pending work
item. This change adds the rotator clock turn off call
when pending work item is freed.

Change-Id: I885c1e88df34caf456e1bd243fb1c57654f4bc4d
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>