pinctrl: ocelot: fix gpio direction

Bits have to be cleared in DEVCPU_GCB:GPIO:GPIO_OE for input and set for
output. ocelot_gpio_set_direction() got it wrong and this went unnoticed
when the driver was reworked.

Reported-by: Gregory Clement <gregory.clement@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>