drm/i915: Missed dropped VMA conversion

This belonged in
commit 07fe0b12800d4752d729d4122c01f41f80a5ba5a
Author: Ben Widawsky <ben@bwidawsk.net>
Date:   Wed Jul 31 17:00:10 2013 -0700

    drm/i915: plumb VM into bind/unbind code

But it was somehow missed along the way.

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

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -307,7 +307,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 	target_i915_obj = target_vma->obj;
 	target_obj = &target_vma->obj->base;
 
-	target_offset = i915_gem_obj_ggtt_offset(target_i915_obj);
+	target_offset = target_vma->node.start;
 
 	/* Sandybridge PPGTT errata: We need a global gtt mapping for MI and
 	 * pipe_control writes because the gpu doesn't properly redirect them