RDMA/mlx5: Fix memory leak in error flow for subscribe event routine

stable inclusion
from stable-v5.10.110
commit c98d903ff9e79c210beddea4e6bc15ac38e25aa5
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c98d903ff9e79c210beddea4e6bc15ac38e25aa5

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[ Upstream commit 087f9c3f ]

In case the second xa_insert() fails, the obj_event is not released.  Fix
the error unwind flow to free that memory to avoid a memory leak.

Fixes: 75973853 ("IB/mlx5: Enable subscription for device events over DEVX")
Link: https://lore.kernel.org/r/1647018361-18266-1-git-send-email-lyz_cs@pku.edu.cn


Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>