net/mlx5e: Fix error flow in tx reporter diagnose

Fix tx reporter's diagnose callback. Propagate error when failing to
gather diagnostics information or failing to print diagnostic data per
queue.

Fixes: de8650a8

 ("net/mlx5e: Add tx reporter support")
Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>