RDMA/core: Fix error return in _ib_modify_qp()

RDMA/core: Fix error return in _ib_modify_qp()

[ Upstream commit 5333499c6014224756e97fa1a1047dfa592d76d3 ]

Fix to return error code PTR_ERR() from the error handling case instead of
0.

Fixes: 51aab12631dd ("RDMA/core: Get xmit slave for LAG")
Link: https://lore.kernel.org/r/20201016075845.129562-1-jingxiangfeng@huawei.com
Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>