vfio-ccw: Set pa_nr to 0 if memory allocation fails for pa_iova_pfn

So we don't call try to call vfio_unpin_pages() incorrectly.

Fixes: 0a19e61e6d ("vfio: ccw: introduce channel program interfaces")
Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <33a89467ad6369196ae6edf820cbcb1e2d8d050c.1562854091.git.alifm@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

drivers/s390/cio/vfio_ccw_cp.c

@@ -72,8 +72,10 @@ static int pfn_array_alloc(struct pfn_array *pa, u64 iova, unsigned int len)
 				  sizeof(*pa->pa_iova_pfn) +
 				  sizeof(*pa->pa_pfn),
 				  GFP_KERNEL);
-	if (unlikely(!pa->pa_iova_pfn))
+	if (unlikely(!pa->pa_iova_pfn)) {
+		pa->pa_nr = 0;
 		return -ENOMEM;
+	}
 	pa->pa_pfn = pa->pa_iova_pfn + pa->pa_nr;
 
 	pa->pa_iova_pfn[0] = pa->pa_iova >> PAGE_SHIFT;