IB/qib: Correct nfreectxts for multiple HCAs

The code that was recently introduced to report the number
of free contexts is flawed for multiple HCAs:

       /* Return the number of free user ports (contexts) available. */
       return scnprintf(buf, PAGE_SIZE, "%u\n", dd->cfgctxts -
                dd->first_user_ctxt - (u32)qib_stats.sps_ctxts);

The qib_stats is global to the module, not per HCA, so the code is broken
for multiple HCAs.

This patch adds a qib_devdata field, freectxts, that reflects the free
contexts for this HCA.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Reviewed-by: Ram Vepa <ram.vepa@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/qib/qib_sysfs.c

@@ -515,8 +515,7 @@ static ssize_t show_nfreectxts(struct device *device,
 	struct qib_devdata *dd = dd_from_dev(dev);
 
 	/* Return the number of free user ports (contexts) available. */
-	return scnprintf(buf, PAGE_SIZE, "%u\n", dd->cfgctxts -
-		dd->first_user_ctxt - (u32)qib_stats.sps_ctxts);
+	return scnprintf(buf, PAGE_SIZE, "%u\n", dd->freectxts);
 }
 
 static ssize_t show_serial(struct device *device,