Use the correct logic to check for the presence of a PHY device, and
jump to a label that correctly releases RTNL in case of an error, as we
are holding RTNL at that point.
Fixes: 3688ff3077d3 ("net: ethtool: cable-test: Target the command to the requested PHY")
Closes: https://lore.kernel.org/netdev/20240827104825.5cbe0602@xxxxxxxxxxxxx/T/#m6bc49cdcc5cfab0d162516b92916b944a01c833f
Signed-off-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>