iio: adc: ti-ads7950: normalize return value of gpio_get

iio: adc: ti-ads7950: normalize return value of gpio_get

The GPIO get callback is expected to return 0 or 1 (or a negative error
code). Ensure that the value returned by ti_ads7950_get() for output
pins is normalized to the [0, 1] range.

Fixes: 86ef402d805d ("gpiolib: sanitize the return value of gpio_chip::get()")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>