drm/msm/dp: fix HDCP error handling

Fix the HDCP error handling by removing a call to destroy
the shared workqueue. The shared workqueue is needed for
other driver events and is destroyed only when the driver
is being removed.

Change-Id: I568d45fab0580870382c4386814560c88d1902f4
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>