Current code test wrong value so it does not verify if the written
data is correctly read back. Fix it.
Also make it return -EPERM if read value does not match written bit,
just like it done for adnp_gpio_direction_output().

Fixes: 5e969a40 ("gpio: Add Avionic Design N-bit GPIO expander support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>