msm: vidc: Always de-assert and assert video_core_clk

As part of the Venus GDSC workaround for MDP on V2, video driver
de-asserts/asserts the video core clk during regulator enable/disable.
Suppose the first video session starts and completes when MDP is awake,
then video driver will assert the core clk when firmware is unloaded.
If a new video session starts after MDP has gone to sleep, then MDP is
no longer voting for venus gdsc and hence video driver does not
de-assert the core clock. Due to this, video core clk does not get enabled
even after regulator is turned ON. Consequently any venus register
read/write will result in unclocked access and crash the device. This
patch ensures that video core clk is always de-asserted prior to
clk_enable.

Change-Id: I2d412b912946d296e3f1120288ff4c77260209a0
Signed-off-by: Arun Menon <avmenon@codeaurora.org>