net/mlx5: Avoid disabling RoCE when uninitialized

Move the check if RoCE steering is initialized to the
disable RoCE function, it will ensure that we disable
RoCE only if we succeeded in enabling it before.

Fixes: 80f09dfc

 ("net/mlx5: Eswitch, enable RoCE loopback traffic")
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>