net: usb: lan78xx: Improve error handling in dataport and multicast writes

net: usb: lan78xx: Improve error handling in dataport and multicast writes

Update `lan78xx_dataport_write` and `lan78xx_deferred_multicast_write`
to:
- Handle errors during register read/write operations.
- Exit immediately on errors and log them using `%pe` for clarity.
- Avoid silent failures by propagating error codes properly.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241204084142.1152696-11-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>