tests: drivers: gpio basic pass testcase when test pin_get is not defined

When the CONFIG_GPIO_GET_CONFIG is set, even if the driver does not
provide the pin_get_config function, it is supposed to return -ENOSYS
error code (see zephyr/include/zephyr/drivers/gpio.h)
The testcase should accept this code and PASS.
(ENOTSUP is not the right value to check).

Signed-off-by: Francois Ramu <francois.ramu@st.com>