xfs: minimal conversion to errseq_t writeback error reporting

Just check and advance the data errseq_t in struct file before
before returning from fsync on normal files. Internal filemap_*
callers are left as-is.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jeff Layton <jlayton@redhat.com>