[PATCH -next] btrfs: qgroup: Fix inconsistent IS_ERR and PTR_ERR

[YueHaibing]

Change the call to PTR_ERR to access the value just tested by IS_ERR.

Fixes: 2b35a512e9cf ("btrfs: qgroup: Use delayed subtree rescan for balance")
Signed-off-by: YueHaibing <yuehaib...@huawei.com>
---
 fs/btrfs/qgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 8559ed9..16d7ec8 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3931,7 +3931,7 @@ int btrfs_qgroup_trace_subtree_after_cow(struct 
btrfs_trans_handle *trans,
                                   block->reloc_generation, block->level,
                                   &block->first_key);
        if (IS_ERR(reloc_eb)) {
-               ret = PTR_ERR(subv_eb);
+               ret = PTR_ERR(reloc_eb);
                reloc_eb = NULL;
                goto free_out;
        }