net/mlx5: fix comments mixing Rx and Tx

net/mlx5: fix comments mixing Rx and Tx

In mlx5_rxq.c, in some comments, text includes "Tx" instead of "Rx".
In mlx5_txq.c, in some comments, text includes "Rx" instead of "Tx".

This patch fixes these typos.

Fixes: faf2667fe8d5 ("net/mlx5: separate DPDK from verbs Tx queue objects")
Fixes: a1366b1a2be3 ("net/mlx5: add reference counter on DPDK Rx queues")
Cc: stable@dpdk.org
Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Shahaf Shuler <shahafs@mellanox.com>