drm/atmel-hlcdc: Fix output initialization

drm_of_find_panel_or_bridge() is expecting np to point to the encoder
node, not the bridge or panel this encoder is feeding.
Moreover, the endpoint parameter passed to drm_of_find_panel_or_bridge()
is always set to zero, which prevents us from probing all outputs.

We also move the atmel_hlcdc_rgb_output allocation after the
panel/bridge detection to avoid useless allocations.

Reported-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Fixes: ebc94461

 ("drm: convert drivers to use drm_of_find_panel_or_bridge")
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1495110921-4032-1-git-send-email-boris.brezillon@free-electrons.com