vdpa: potential uninitialized return in vhost_vdpa_va_map()

The concern here is that "ret" can be uninitialized if we hit the
"goto next" condition on every iteration through the loop.

Fixes: 41ba1b5f9d4b ("vdpa: Support transferring virtual addressing during DMA mapping")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20210907073253.GB18254@kiliSigned-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NXie Yongji <xieyongji@bytedance.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NStefano Garzarella <sgarzare@redhat.com>

drivers/vhost/vdpa.c

@@ -640,7 +640,7 @@ static int vhost_vdpa_va_map(struct vhost_vdpa *v,
 	u64 offset, map_size, map_iova = iova;
 	struct vdpa_map_file *map_file;
 	struct vm_area_struct *vma;
-	int ret;
+	int ret = 0;
 
 	mmap_read_lock(dev->mm);