IB/ipath: Shared context code needs to be sure device is usable

The code was checking if units are present, but not that present units
were usable (link up, etc.)
Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/ipath/ipath_file_ops.c

@@ -1760,7 +1760,7 @@ static int find_shared_port(struct file *fp,
 	for (ndev = 0; ndev < devmax; ndev++) {
 		struct ipath_devdata *dd = ipath_lookup(ndev);
 
-		if (!dd)
+		if (!usable(dd))
 			continue;
 		for (i = 1; i < dd->ipath_cfgports; i++) {
 			struct ipath_portdata *pd = dd->ipath_pd[i];