pinctrl: berlin: fix an error code in berlin_pinctrl_probe()

We are returning success here because PTR_ERR(NULL) is zero.  We should
be returning -ENODEV.

Fixes: 3de68d33 ('pinctrl: berlin: add the core pinctrl driver for Marvell Berlin SoCs')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>