drm/msm/dp: do not execute hdcp work if aborted

The HDCP sub-module responds with the authentication status
which is queued on a worker thread in DP display sub-module
for further processing. In case DP cable is disconnected or
the DP controller is powered off, it may result in unstable
state. Check for DP state before processing HDCP response
to avoid possible race condition which can lead to unstable
behavior.

Change-Id: I1b3f20da5a6fb35c70ad6e09652c6b236efd0e42
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>