xfs_reflink_cancel_cow_range joins an inode twice to the same
transaction.  This is not allowed, so fix it and document that the
callers of xfs_reflink_cancel_cow_blocks() must have already joined the
inode to the permanent transaction passed in.
Signed-Off-By: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
[darrick: edited the commit log to remove trace for nonexistent ASSERT]
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>