msm: mdss: propagate error in case of panel on failure

There are cases in which panel on can fail for any reason, such as
unable to properly get and lock on to hardware resources. For such cases
the error needs to be properly propagated so that the state of MDP can
be reset and user space application can invoke some recovery mechanism.

Change-Id: I0da17038e11e6b972740dd6362c1a75bd2bd2b28
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>