pinctrl: berlin: fix error return code of berlin_pinctrl_build_state()

When krealloc() fails and pctrl->functions is NULL, no error
return code of berlin_pinctrl_build_state() is assigned.
To fix this bug, ret is assigned with -ENOMEM when pctrl->functions
is NULL.

Signed-off-by: Meng Tang <tangmeng@uniontech.com>
Link: https://lore.kernel.org/r/20220303080206.16463-1-tangmeng@uniontech.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>