drm/i915: Cleanup error paths through eb_lookup_vma()

Following the simplification to a single lookup loop in commit
170fa29b14fa ("drm/i915: Simplify eb_lookup_vmas()") and commit
d1b48c1e7184 ("drm/i915: Replace execbuf vma ht with an idr"), we can go
one step further and reorder the error paths so that the state of the
local variable obj is always known to the compiler and doesn't need the
uninitialized_var markup to squelch a compiler warning.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170912150752.20411-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -679,7 +679,7 @@ static int eb_select_context(struct i915_execbuffer *eb)
 static int eb_lookup_vmas(struct i915_execbuffer *eb)
 {
 	struct radix_tree_root *handles_vma = &eb->ctx->handles_vma;
-	struct drm_i915_gem_object *uninitialized_var(obj);
+	struct drm_i915_gem_object *obj;
 	unsigned int i;
 	int err;
 
@@ -725,19 +725,17 @@ static int eb_lookup_vmas(struct i915_execbuffer *eb)
 			goto err_obj;
 		}
 
+		/* transfer ref to ctx */
 		vma->open_count++;
 		list_add(&lut->obj_link, &obj->lut_list);
 		list_add(&lut->ctx_link, &eb->ctx->handles_list);
 		lut->ctx = eb->ctx;
 		lut->handle = handle;
 
-		/* transfer ref to ctx */
-		obj = NULL;
-
 add_vma:
 		err = eb_add_vma(eb, i, vma);
 		if (unlikely(err))
-			goto err_obj;
+			goto err_vma;
 
 		GEM_BUG_ON(vma != eb->vma[i]);
 		GEM_BUG_ON(vma->exec_flags != &eb->flags[i]);
@@ -766,8 +764,7 @@ add_vma:
 	return eb_reserve(eb);
 
 err_obj:
-	if (obj)
-		i915_gem_object_put(obj);
+	i915_gem_object_put(obj);
 err_vma:
 	eb->vma[i] = NULL;
 	return err;