drm/i915: Initialize return value for empty i915_gem_object_unbind()

If the obj->vma_list is empty, we immediately return ret. However, we
are doing so having never set it to any value, it should be zero!
Reported-by: Matthew Auld <matthew.auld@intel.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=97343
Fixes: aa653a68 ("drm/i915: Be more careful when unbinding vma")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471196681-30043-1-git-send-email-chris@chris-wilson.co.ukReviewed-by: Matthew Auld <matthew.auld@intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -279,12 +279,11 @@ static const struct drm_i915_gem_object_ops i915_gem_phys_ops = {
 	.release = i915_gem_object_release_phys,
 };
 
-int
-i915_gem_object_unbind(struct drm_i915_gem_object *obj)
+int i915_gem_object_unbind(struct drm_i915_gem_object *obj)
 {
 	struct i915_vma *vma;
 	LIST_HEAD(still_in_list);
-	int ret;
+	int ret = 0;
 
 	/* The vma will only be freed if it is marked as closed, and if we wait
 	 * upon rendering to the vma, we may unbind anything in the list.