net: usb: lan78xx: Improve error reporting with %pe specifier

Replace integer error codes with the `%pe` format specifier in register
read and write error messages. This change provides human-readable error
strings, making logs more informative and debugging easier.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241204084142.1152696-5-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/usb/lan78xx.c

@@ -621,8 +621,8 @@ static int lan78xx_read_reg(struct lan78xx_net *dev, u32 index, u32 *data)
 		*data = *buf;
 	} else if (net_ratelimit()) {
 		netdev_warn(dev->net,
-			    "Failed to read register index 0x%08x. ret = %d",
-			    index, ret);
+			    "Failed to read register index 0x%08x. ret = %pe",
+			    index, ERR_PTR(ret));
 	}
 
 	kfree(buf);
@@ -652,8 +652,8 @@ static int lan78xx_write_reg(struct lan78xx_net *dev, u32 index, u32 data)
 	if (unlikely(ret < 0) &&
 	    net_ratelimit()) {
 		netdev_warn(dev->net,
-			    "Failed to write register index 0x%08x. ret = %d",
-			    index, ret);
+			    "Failed to write register index 0x%08x. ret = %pe",
+			    index, ERR_PTR(ret));
 	}
 
 	kfree(buf);