net: ag71xx: remove dead code path

The "err" is always zero, so the following branch can never be executed:
if (err) {
	ndev->stats.rx_dropped++;
	kfree_skb(skb);
}
Therefore, the "if" statement can be removed.

Use "ndev->stats.rx_errors" to count "napi_build_skb()" failure

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/20240911135828.378317-1-usama.anjum@collabora.com


Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com>
Link: https://patch.msgid.link/20240913014731.149739-1-qianqiang.liu@163.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>