i915: add missing return in error path.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 6a89449..a31ee32 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -146,6 +146,7 @@
 	if (ret != 0) {
 		drm_gem_object_unreference(obj);
 		mutex_unlock(&dev->struct_mutex);
+		return ret;
 	}
 
 	offset = args->offset;