Jesse's BIOS fb reconstruction code actually relies on the -ENOSPC
return value to detect overlapping framebuffers (which the bios uses
always when lighting up more than one screen). All this fanciness
happens in intel_alloc_plane_obj in intel_display.c.

Since no one else uses this we can safely remove the WARN without
repercussions.
Reported-by: NBen Widawsky <benjamin.widawsky@intel.com>
Tested-by: NBen Widawsky <ben@bwidawsk.net>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: NDave Airlie <airlied@redhat.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>