net/mlx5e: Fix compilation warning in en_tc.c

Amazingly a mlx5e_tc function is being called from the eswitch layer,
which is by itself very terrible! The function was declared locally in
eswitch_offloads.c so it could be used there, which caused the following
compilation warning, fix that.

drivers/.../mlx5/core/en_tc.c:3242:6: [-Werror=missing-prototypes]
error: no previous prototype for ‘mlx5e_tc_clean_fdb_peer_flows’

Fixes: 04de7dda ("net/mlx5e: Infrastructure for duplicated offloading of TC flows")
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>