iio: adc: ti-ads7950: do not clobber gpio state in ti_ads7950_get()

iio: adc: ti-ads7950: do not clobber gpio state in ti_ads7950_get()

GPIO state was inadvertently overwritten by the result of spi_sync(),
resulting in ti_ads7950_get() only returning 0 as GPIO state (or error).

Fix this by introducing a separate variable to hold the state.

Fixes: c97dce792dc8 ("iio: adc: ti-ads7950: add GPIO support")
Reported-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>