mlxsw: core: use PSID string define in devlink info

Instead of having the string spelled out in the driver, use the global
define with the same value.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>