drm/msm/sde: propagate kickoff prepare errors to crtc

Report errors during the encoder's prepare for kickoff calls
to the CRTC, so that the CRTC can avoid blindly dispatching
the current commit even in the face of preparation errors.

Change-Id: I3ad5d89877d65ff8d61a20d10a096bc2f3f5601a
Signed-off-by: Clarence Ip <cip@codeaurora.org>