arm64: a37xx: dts: Fix the number of GPIO on south bridge

arm64: a37xx: dts: Fix the number of GPIO on south bridge

The number of pins in South Bridge is 30 and not 29. There is a fix for
the driver for the pinctrl, but a fix is also need at device tree level
for the GPIO.

Reviewed-on: http://vgitil04.il.marvell.com:8080/43286
Reviewed-by: Hua Jing <[email protected]>
Tested-by: iSoC Platform CI <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Stefan Roese <[email protected]>
Signed-off-by: Ken Ma <[email protected]>
Signed-off-by: Stefan Roese <[email protected]>