drm/msm: handle case where atomic dispatch fails

Handle the case where dispatch to a specific CRTC fails,
possibly due to receiving an empty commit, by doing a
synchronous commit in place. This is necessary since the state
has already been swapped, and so it is not valid to free the
atomic state.

Change-Id: I051794e2afd533cc563c4285ce5a417f28a90cd3
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>