net: phy: Fix unsigned comparison with less than zero

Fix the following coccicheck warning:

./drivers/net/phy/at803x.c:493:5-10: WARNING: Unsigned expression
compared with zero: value < 0.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Fixes: 7beecaf7 ("net: phy: at803x: improve the WOL feature")
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/1635325191-101815-1-git-send-email-jiapeng.chong@linux.alibaba.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/at803x.c

@@ -484,7 +484,7 @@ static int at803x_set_wol(struct phy_device *phydev,
 static void at803x_get_wol(struct phy_device *phydev,
 			   struct ethtool_wolinfo *wol)
 {
-	u32 value;
+	int value;
 
 	wol->supported = WAKE_MAGIC;
 	wol->wolopts = 0;