ethtool: pse-pd: Fix double word in comments

Remove the repeated word "for" in comments.
Signed-off-by: Bo Liu <liubo03@inspur.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20230221083036.2414-1-liubo03@inspur.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/pse-pd.c

 // SPDX-License-Identifier: GPL-2.0-only
 //
-// ethtool interface for for Ethernet PSE (Power Sourcing Equipment)
+// ethtool interface for Ethernet PSE (Power Sourcing Equipment)
 // and PD (Powered Device)
 //
 // Copyright (c) 2022 Pengutronix, Oleksij Rempel <kernel@pengutronix.de>