arm64: dts: marvell: fix number of GPIOs in Armada AP806 description

The Armada AP806 has 20 pins, and therefore 20 GPIOs (from 0 to 19
included) and not 19 pins. Therefore, we fix the Device Tree
description for the GPIO controller.

Before this patch:

$ cat /sys/kernel/debug/pinctrl/f06f4000.system-controller:pinctrl/gpio-ranges
GPIO ranges handled:
0: mvebu-gpio GPIOS [0 - 19] PINS [0 - 19]
0: f06f4000.system-controller:gpio GPIOS [0 - 18] PINS [0 - 18]

After this patch:

$ cat /sys/kernel/debug/pinctrl/f06f4000.system-controller:pinctrl/gpio-ranges
GPIO ranges handled:
0: mvebu-gpio GPIOS [0 - 19] PINS [0 - 19]
0: f06f4000.system-controller:gpio GPIOS [0 - 19] PINS [0 - 19]

Fixes: 63dac0f4

 ("arm64: dts: marvell: add gpio support for Armada 7K/8K")
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>