drm/i915: checking IS_ERR() instead of NULL

We switched from calling i915_gem_alloc_context_obj() to calling
i915_gem_alloc_object() so the error handling needs to be updated to
check for NULL instead of IS_ERR().

Fixes: 149c86e7 ('drm/i915: Allocate context objects from stolen')
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -1895,10 +1895,9 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
 	context_size = round_up(get_lr_context_size(ring), 4096);
 
 	ctx_obj = i915_gem_alloc_object(dev, context_size);
-	if (IS_ERR(ctx_obj)) {
-		ret = PTR_ERR(ctx_obj);
-		DRM_DEBUG_DRIVER("Alloc LRC backing obj failed: %d\n", ret);
-		return ret;
+	if (!ctx_obj) {
+		DRM_DEBUG_DRIVER("Alloc LRC backing obj failed.\n");
+		return -ENOMEM;
 	}
 
 	if (is_global_default_ctx) {