Fix broken iio_device_get_sample_size with same-index channels
Fix broken iio_device_get_sample_size with same-index channels

This fixes a bug introduced in 4792fa3.

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio