BGPIO_F_UNREADABLE_REG_SET is incorrect, since the set register _is_
readable. What's really required is BGPIO_F_READ_OUTPUT_REG_SET:
reading the set register reads the set output value.
Signed-off-by: Rabin Vincent <rabin@rab.in> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>