RDMA/mlx5: Fix validation of max_rd_atomic caps for DC

Currently, when modifying DC, we validate max_rd_atomic user attribute
against the RC cap, validate against DC. RC and DC QP types have different
device limitations.

This can cause userspace created DC QPs to malfunction.

Fixes: c32a4f29 ("IB/mlx5: Add support for DC Initiator QP")
Link: https://lore.kernel.org/r/0c5aee72cea188c3bb770f4207cce7abc9b6fc74.1672231736.git.leonro@nvidia.com


Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>