net/mlx5: Avoid deriving mlx5_core_dev second time

All callers needs to work on mlx5_core_dev and it is already derived
before calling mlx5_devlink_eswitch_check().
Hence, accept mlx5_core_dev in mlx5_devlink_eswitch_check().

Given that it works on mlx5_core_dev change helper function name to
drop devlink prefix.

Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>