pinctrl: armada-37xx: Fix number of pin in sdio_sb

The sdio_sb group is composed of 6 pins and not 5.

Reported-by: Ken Ma <make@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>