net/mlx5: DR, Fix getting incorrect prev node in ste_free

When we free an STE and the STE is in the middle of collision
list, the prev_ste was obtained incorrectly from the list.
To avoid such issues list_entry calls replaced with standard list API.

Fixes: 26d688e3 ("net/mlx5: DR, Add Steering entry (STE) utilities")
Signed-off-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>