net: gianfar: fix device leak when querying time stamp info

commit da717540acd34e5056e3fa35791d50f6b3303f55 upstream.

Make sure to drop the reference to the ptp device taken by
of_find_device_by_node() when querying the time stamping capabilities.

Note that holding a reference to the ptp device does not prevent its
driver data from going away.

Fixes: 7349a74e ("net: ethernet: gianfar_ethtool: get phc index through drvdata")
Cc: stable@vger.kernel.org	# 4.18
Cc: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250725171213.880-4-johan@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>