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_init.c b/drivers/infiniband/hw/qib/qib_init.c
index a01f3fc..021636d 100644
--- a/drivers/infiniband/hw/qib/qib_init.c
+++ b/drivers/infiniband/hw/qib/qib_init.c
@@ -398,6 +398,7 @@
 		if (rcd)
 			dd->f_rcvctrl(rcd->ppd, rcvmask, i);
 	}
+	dd->freectxts = dd->cfgctxts - dd->first_user_ctxt;
 }
 
 static void verify_interrupt(unsigned long opaque)