Make intel_render_ring_init_dri and intel_init_ring_buffer symmetrical
with regards of workaround introduced by:
commit 
27c1cbd06a7620b354cbb363834f3bb8df4f410d
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Apr 9 13:59:46 2012 +0100
    drm/i915/ringbuffer: Exclude last 2 cachlines of ring on 845g
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
 
        ring->size = size;
        ring->effective_size = ring->size;
-       if (IS_I830(ring->dev))
+       if (IS_I830(ring->dev) || IS_845G(ring->dev))
                ring->effective_size -= 128;
 
        ring->virtual_start = ioremap_wc(start, size);