pinctrl-baytrail: fix to avoid sparse warnings

There are couple of sparse warnings we could avoid if we use a bit verbose
version of the code in byt_gpio_direction_output().

drivers/pinctrl/pinctrl-baytrail.c:266:45: warning: dubious: x | !y
drivers/pinctrl/pinctrl-baytrail.c:267:36: warning: dubious: x | !y

Additionally simplify a bit the code in byt_gpio_direction_input().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>