drm/i915/bdw: Take render error interrupt out of the mask

The handling of the error interrupts isn't wired up at all. And it
hasn't been ever since ilk happened, so don't bother.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/intel_ringbuffer.c
Simple merge