RDMA/erdma: Correct the max_qp and max_cq capacities of the device

QP0 in HW is used for CMDQ, and the rest is for RDMA QPs. So the actual
max_qp capacity reported to core should be max_qp (reported by HW) - 1.
So does max_cq.

Fixes: 15505577

 ("RDMA/erdma: Add verbs implementation")
Link: https://lore.kernel.org/all/20220810014320.88026-1-chengyou@linux.alibaba.com
Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>