imx-drm: parallel-display: Fix DPMS default state.

If connector->dpms is left untouched, it defaults
to DRM_MODE_DPMS_ON (0).

As a result, drm_helper_connector_dpms will exit when
it will be asked to set the state to DRM_MODE_DPMS_ON,
because it is already set.

That issue prevented displays from turning on at boot.

Signed-off-by: Denis Carikli <denis@eukrea.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>