rtc: pcf8563: use correct of_node for output clock

rtc: pcf8563: use correct of_node for output clock

When switching to regmap, the i2c_client pointer was removed from struct
pcf8563 so this function switched to using the RTC device instead.  But
the RTC device is a child of the original I2C device and does not have
an associated of_node.

Reference the correct device's of_node to ensure that the output clock
can be found when referenced by other devices and so that the override
clock name is read correctly.

Cc: stable@vger.kernel.org
Fixes: 00f1bb9b8486b ("rtc: pcf8563: Switch to regmap")
Signed-off-by: John Keeping <jkeeping@inmusicbrands.com>
Link: https://patch.msgid.link/20260108184749.3413348-1-jkeeping@inmusicbrands.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>