gpio: use (!foo) instead of (foo == NULL)

Signed-off-by: Varka Bhadram <varkab@cdac.in>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

diff --cc drivers/gpio/gpio-adp5588.c
Simple merge

diff --cc drivers/gpio/gpio-arizona.c
Simple merge

diff --cc drivers/gpio/gpio-da9052.c
Simple merge

diff --cc drivers/gpio/gpio-da9055.c
Simple merge

diff --cc drivers/gpio/gpio-kempld.c
Simple merge

diff --cc drivers/gpio/gpio-mc33880.c
Simple merge