Blanking On/Off calls should not return 0 when there is no panel
controller to forward them to, instead they should return ENOSYS to
signal to the application that they were not actually executed.
"device_is_ready" does check for null, but also for
"dev->state->initialized == false", so we need to isolate the
"dev == NULL" case.
Signed-off-by: Abderrahmane Jarmouni <git@jarmouni.me>
(cherry picked from commit f7de44dfaf)
