drm: fixup i915 breadcrumb read/write

Some minor issues in the i915 breadcrumb code.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/i915_dma.c

@@ -495,8 +495,6 @@ static int i915_dispatch_batchbuffer(drm_device_t * dev,
 		}
 	}
 
-	dev_priv->sarea_priv->last_enqueue = dev_priv->counter++;
-
 	i915_emit_breadcrumb(dev);
 
 	return 0;