RDMA/mlx5: Initialize return variable in case pagefault was skipped

mainline inclusion
from mainline-4.20-rc7
commit 7bca603a69c0c239654a8f0bcb99e1a60b30040c
category: bugfix
bugzilla: 6625
CVE: NA

-----------------------------

Since any page fault may be interrupted by a MMU invalidation and implicit
Pagefaults occurred in non-ODP MR are completely valid events, so
initialize return variable to 0.

Fixes: 4d5422a309de ("IB/mlx5: Skip non-ODP MR when handling a page fault")
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: NJing Xiangfeng <jingxiangfeng@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/infiniband/hw/mlx5/odp.c

@@ -668,6 +668,7 @@ static int pagefault_single_data_segment(struct mlx5_ib_dev *dev,
 				    key);
 			if (bytes_mapped)
 				*bytes_mapped += bcnt;
+			ret = 0;
 			goto srcu_unlock;
 		}