Btrfs: avoid warning bomb of btrfs_invalidate_inodes

So after transaction is aborted, we need to cleanup inode resources by
calling btrfs_invalidate_inodes(), and btrfs_invalidate_inodes() hopes
roots' refs to be zero in old times and sets a WARN_ON(), however, this
is not always true within cleaning up transaction, so we get to detect
transaction abortion and not warn at all.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b88f622..8dba152 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4926,7 +4926,8 @@
 	struct inode *inode;
 	u64 objectid = 0;
 
-	WARN_ON(btrfs_root_refs(&root->root_item) != 0);
+	if (!test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
+		WARN_ON(btrfs_root_refs(&root->root_item) != 0);
 
 	spin_lock(&root->inode_lock);
 again: