regulator: mt6370: Use 'fwnode_gpiod_get_index' to fix gpio parsing

regulator: mt6370: Use 'fwnode_gpiod_get_index' to fix gpio parsing

From the common binding, 'enable-gpio' or 'enable-gpios' are all well
for external 'enable' gpio.

'gpiod_get_from_of_node' only parse the 'enable' property, it need to
add the gpio suffix. It's more convenient to use fwnode_gpiod_get_index.
Although fwnode parsing is not preferred, but 'of_parse_cb' already can
guarantee the callback will only be used by regulator of_node parsing.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/1656466861-7737-1-git-send-email-u0084500@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>