IB/mlx5: Add missing error code

stable inclusion
from stable-5.10.22
commit 7ef9d23bc3121be3e77ed7fbcf9d3c9ecbf7005e
bugzilla: 50796

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

[ Upstream commit 3a9b3d45 ]

Set err to -ENOMEM if kzalloc fails instead of 0.

Fixes: 75973853 ("IB/mlx5: Enable subscription for device events over DEVX")
Link: https://lore.kernel.org/r/20210222122343.19720-1-yuehaibing@huawei.com


Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by:   Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>