Update the output pin name that enables reading RTC battery voltage.

Link: https://github.com/openbmc/docs/blob/master/designs/device-tree-gpio-naming.md#rtc-battery-voltage-read-enableSigned-off-by: Quan Nguyen <quan@os.amperecomputing.com>
Signed-off-by: Thang Q. Nguyen <thang@os.amperecomputing.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20220228000242.1884-3-quan@os.amperecomputing.comSigned-off-by: Joel Stanley <joel@jms.id.au>