There is an empty "all good" branch in sas_check_parent_topology(). We can
reverse the test statement and remove the empty branch.

Moreover, factor out a helper sas_check_edge_expander_topo() to make the
code more readable.
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20230421093744.1583609-3-yanaijie@huawei.comReviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>