mlxsw: Add return value check for mlxsw_sp_port_get_stats_raw()

Add a check for the return value of mlxsw_sp_port_get_stats_raw()
in __mlxsw_sp_port_get_stats(). If mlxsw_sp_port_get_stats_raw()
returns an error, exit the function to prevent further processing
with potentially invalid data.

Fixes: 614d509aa1e7 ("mlxsw: Move ethtool_ops to spectrum_ethtool.c")
Cc: [e-mail] # 5.9+
Signed-off-by: Wentao Liang <[e-mail]>
Reviewed-by: Petr Machata <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c

···
 	err = mlxsw_sp_get_hw_stats_by_group(&hw_stats, &len, grp);
 	if (err)
 		return;
-	mlxsw_sp_port_get_stats_raw(dev, grp, prio, ppcnt_pl);
+	err = mlxsw_sp_port_get_stats_raw(dev, grp, prio, ppcnt_pl);
+	if (err)
+		return;
 	for (i = 0; i < len; i++) {
 		data[data_index + i] = hw_stats[i].getter(ppcnt_pl);
 		if (!hw_stats[i].cells_bytes)