net/mlx5: Add esw assignment back in mlx5e_tc_sample_unoffload()

Clang warns:

drivers/net/ethernet/mellanox/mlx5/core/en/tc/sample.c:635:34: error: variable 'esw' is uninitialized when used here [-Werror,-Wuninitialized]
        mlx5_eswitch_del_offloaded_rule(esw, sample_flow->pre_rule, sample_flow->pre_attr);
                                        ^~~
drivers/net/ethernet/mellanox/mlx5/core/en/tc/sample.c:626:26: note: initialize the variable 'esw' to silence this warning
        struct mlx5_eswitch *esw;
                                ^
                                 = NULL
1 error generated.

It appears that the assignment should have been shuffled instead of
removed outright like in mlx5e_tc_sample_offload(). Add it back so there
is no use of esw uninitialized.

Fixes: a64c5edb

 ("net/mlx5: Remove unnecessary checks for slow path flag")
Link: https://github.com/ClangBuiltLinux/linux/issues/1494
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>