drm/i915: Update missing properties in find_initial_plane_obj

The src and crtc rectangles were never set, resulting in the primary
plane being made invisible on first atomic update.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>