drm/arm: mali-dp: Set crtc.port to the port instead of the endpoint

The CRTC's port pointer was being set to the endpoint node instead of
the port. Fix that, and hold a reference on the port node.

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
Acked-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1469549725-19577-1-git-send-email-brian.starkey@arm.com