gpio: 74xx-mmio: Check MMIO_74XX_DIR_IN flag in mmio_74xx_dir_in()

It's logically better to check the IN in ->direction_input() and
_OUT in ->direction_output().

While at it, replace ternary with plain if-conditional for the sake
of consistency with mmio_74xx_dir_out().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>