arm64: a37xx: pinctrl: Fix number of pin in south bridge

On the south bridge we have pin from 0 to 29, so it gives 30 pins (and
not 29).

Reviewed-on: http://vgitil04.il.marvell.com:8080/43285


Tested-by: iSoC Platform CI <ykjenk@marvell.com>
Reviewed-by: Hua Jing <jinghua@marvell.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Ken Ma <make@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>