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>
diff --git a/drivers/infiniband/hw/qib/qib_file_ops.c b/drivers/infiniband/hw/qib/qib_file_ops.c
index 2625303..7763366 100644
--- a/drivers/infiniband/hw/qib/qib_file_ops.c
+++ b/drivers/infiniband/hw/qib/qib_file_ops.c
@@ -1284,6 +1284,7 @@
 	strlcpy(rcd->comm, current->comm, sizeof(rcd->comm));
 	ctxt_fp(fp) = rcd;
 	qib_stats.sps_ctxts++;
+	dd->freectxts++;
 	ret = 0;
 	goto bail;
 
@@ -1792,6 +1793,7 @@
 		if (dd->pageshadow)
 			unlock_expected_tids(rcd);
 		qib_stats.sps_ctxts--;
+		dd->freectxts--;
 	}
 
 	mutex_unlock(&qib_mutex);