IB/srpt: Remove WARN_ON from srpt_cm_req_recv

IB/srpt: Remove WARN_ON from srpt_cm_req_recv

The callers pass the pointer '&req' or 'private_data' to
srpt_cm_req_recv(), and 'private_data' is initialized in srp_send_req().
'sdev' is allocated and stored in srpt_add_one(). It's easy to show that
sdev and req are always valid. So we remove unnecessary WARN_ON.

Link: https://lore.kernel.org/r/20200617140803.181333-1-jingxiangfeng@huawei.com
Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>