block: Don't use error_abort in blk_new_open

We have an errp and bdrv_root_attach_child can fail permission check,
error_abort is not the best choice here.
Signed-off-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -213,7 +213,12 @@ BlockBackend *blk_new_open(const char *filename, const char *reference,
     }
 
     blk->root = bdrv_root_attach_child(bs, "root", &child_root,
-                                       perm, BLK_PERM_ALL, blk, &error_abort);
+                                       perm, BLK_PERM_ALL, blk, errp);
+    if (!blk->root) {
+        bdrv_unref(bs);
+        blk_unref(blk);
+        return NULL;
+    }
 
     return blk;
 }