net: ena: removed unused tx_bytes variable

clang 16.0.0 with W=1 reports:

drivers/net/ethernet/amazon/ena/ena_netdev.c:1901:6: error: variable 'tx_bytes' set but not used [-Werror,-Wunused-but-set-variable]
        u32 tx_bytes = 0;

The variable is not used so remove it.
Signed-off-by: Simon Horman <horms@kernel.org>
Acked-by: Shay Agroskin <shayagr@amazon.com>
Link: https://lore.kernel.org/r/20230328151958.410687-1-horms@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/amazon/ena/ena_netdev.c

@@ -1898,7 +1898,6 @@ static int ena_clean_xdp_irq(struct ena_ring *xdp_ring, u32 budget)
 {
 	u32 total_done = 0;
 	u16 next_to_clean;
-	u32 tx_bytes = 0;
 	int tx_pkts = 0;
 	u16 req_id;
 	int rc;
@@ -1936,7 +1935,6 @@ static int ena_clean_xdp_irq(struct ena_ring *xdp_ring, u32 budget)
 			  "tx_poll: q %d skb %p completed\n", xdp_ring->qid,
 			  xdpf);
 
-		tx_bytes += xdpf->len;
 		tx_pkts++;
 		total_done += tx_info->tx_descs;