IB/qib: fix test of unsigned variable

Commit d4988623 ("IB/qib: use arch_phys_wc_add()")
adjusted mtrr inititialization to use the new interface.

Unfortunately, the new interface returns a signed
value and the patch tested the unsigned wc_cookie.

Fix the issue by changing the type of wc_cookie to int.  For
the success case the ret left at zero to avoid
a warning from the caller.  For failure wc_cookie
is used as the ret.
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/qib/qib.h

@@ -903,7 +903,7 @@ struct qib_devdata {
 	/* PCI Device ID (here for NodeInfo) */
 	u16 deviceid;
 	/* for write combining settings */
-	unsigned long wc_cookie;
+	int wc_cookie;
 	unsigned long wc_base;
 	unsigned long wc_len;
 

drivers/infiniband/hw/qib/qib_wc_x86_64.c

@@ -118,7 +118,8 @@ int qib_enable_wc(struct qib_devdata *dd)
 	if (!ret) {
 		dd->wc_cookie = arch_phys_wc_add(pioaddr, piolen);
 		if (dd->wc_cookie < 0)
-			ret = -EINVAL;
+			/* use error from routine */
+			ret = dd->wc_cookie;
 	}
 
 	return ret;