gpio: exar: Fix reading of directions and values

First, the logic for translating a register bit to the return code of
exar_get_direction and exar_get_value were wrong. And second, there was
a flip regarding the register bank in exar_get_direction.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>