net: usb: lan78xx: Add error handling to lan78xx_init_mac_address

Convert `lan78xx_init_mac_address` to return error codes and handle
failures in register read and write operations. Update `lan78xx_reset`
to check for errors during MAC address initialization and propagate them
appropriately.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241209130751.703182-3-o.rempel@pengutronix.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>