vhost: fix error handling for memory region alloc

callers of vhost_kvzalloc() expect the same behaviour on
allocation error as from kmalloc/vmalloc i.e. NULL return
value. So just return vzmalloc() returned value instead of
returning ERR_PTR(-ENOMEM)

Fixes: 4de7255f ("vhost: extend memory regions allocation to vmalloc")
Spotted-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vhost.c

@@ -683,11 +683,8 @@ static void *vhost_kvzalloc(unsigned long size)
 {
 	void *n = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
 
-	if (!n) {
-		n = vzalloc(size);
 	if (!n)
-			return ERR_PTR(-ENOMEM);
-	}
+		n = vzalloc(size);
 	return n;
 }