RDMA/hns: Fix an error code in hns_roce_set_user_sq_size()

This function is supposed to return negative kernel error codes but here
it returns CMD_RST_PRC_EBUSY (2).  The error code eventually gets passed
to IS_ERR() and since it's not an error pointer it leads to an Oops in
hns_roce_v1_rsv_lp_qp()

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>