RDMA/mlx5: Refactor _get_prio() function

RDMA/mlx5: Refactor _get_prio() function

Refactor the _get_prio() function to remove redundant arguments by
reusing the existing flow table attributes struct instead of passing
attributes separately. This improves code clarity and maintainability.

In addition allows downstream patch to add new parameter without
needing to change __get_prio() arguments.

Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/20251029-support-other-eswitch-v1-6-98bb707b5d57@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>