net/mlx5: E-Switch, Fix double mutex initialization

Delete mutex_init call of a lock that's initialized in inner function.

Fixes: eca8cc38 ("net/mlx5: E-Switch, Refactor offloads flow steering init/cleanup")
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>