ARM: dts: aspeed-g6: Fix the GPIO memory size

ARM: dts: aspeed-g6: Fix the GPIO memory size

The GPIO controller is a GPIO controller followed by some SGPIO
controllers, which are a different type of device with their own binding
and drivers.

Make the gpio node cover the only conventional GPIO controller.

Fixes: 8dbcb5b709b9 ("ARM: dts: aspeed-g6: Add gpio devices")
Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20201012033150.21056-2-billy_tsai@aspeedtech.com
Signed-off-by: Joel Stanley <joel@jms.id.au>