gpio: gpio-ucb1400.c: Cleaning up null pointer checks that could never happen

Removal of null pointer checks that could never happen

This was found using a static code analysis program called cppcheck

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>