net: usb: lan78xx: Use action-specific label in lan78xx_mac_reset

Rename the generic `done` label to the action-specific `exit_unlock`
label in `lan78xx_mac_reset`. This improves clarity by indicating the
specific cleanup action (mutex unlock) and aligns with best practices
for error handling and cleanup labels.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Link: https://patch.msgid.link/20241216120941.1690908-4-o.rempel@pengutronix.de


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