net/mlx5: Eswitch, Use 'kvfree()' for memory allocated by 'kvzalloc()'

When 'kvzalloc()' is used to allocate memory, 'kvfree()' must be used to
free it.

Fixes: fed9ce22 ("net/mlx5: E-Switch, Add API to create vport rx rules")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>