net: usb: lan78xx: Add error handling to lan78xx_get_regs

Update `lan78xx_get_regs` to handle errors during register and PHY
reads. Log warnings for failed reads and exit the function early if an
error occurs. Drop all previously logged registers to signal
inconsistent readings to the user space. This ensures that invalid data
is not returned to users.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20241216120941.1690908-2-o.rempel@pengutronix.de


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