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>