staging: iio: resolver: ad2s1210: fix not restoring sample gpio in channel read

In theory, this code path should not be reachable because of the
previous switch statement. But just in case we should make sure we
are restoring the SAMPLE gpio to its original state before returning
in addition to releasing the mutex lock.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20230921144400.62380-5-dlechner@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>