net: usb: lan78xx: Improve error handling in lan78xx_phy_wait_not_busy

net: usb: lan78xx: Improve error handling in lan78xx_phy_wait_not_busy

Update `lan78xx_phy_wait_not_busy` to forward errors from
`lan78xx_read_reg` instead of overwriting them with `-EIO`. Replace
`-EIO` with `-ETIMEDOUT` for timeout cases, providing more specific and
appropriate error codes.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241209130751.703182-10-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>