arm64: dts: zii-ultra: fix ARM regulator GPIO handle

The GPIO handle is referencing the wrong GPIO, so the voltage did not
actually change as intended. The pinmux is already correct, so just
correct the GPIO number.

Fixes: 4a13b3be

 (arm64: dts: imx: add Zii Ultra board support)
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>