net/mlx5e: Apply the correct check for supporting TC esw rules split

The mirror and not the output count is the one denoting a split.
Fix to condition the offload attempt on the mirror count being > 0
along the firmware to have the related capability.

Fixes: 592d3651 ("net/mlx5e: Parse mirroring action for offloaded TC eswitch flows")
Signed-off-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Yossi Kuperman <yossiku@mellanox.com>
Reviewed-by: Chris Mi <chrism@mellanox.com>
Acked-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>