AD7999 fails to measure in kernel 3.17

Kernel version 3.15 with (staging) AD7999 driver:

# cat /sys/bus/iio/devices/iio\:device0/in_voltage*

186

110

124

94

12.890625000

Kernel version 3.17 fails to report the measured voltages, using the same devicetree:

# cat /sys/bus/iio/devices/iio\:device0/in_voltage*

255

255

255

255

12.890625000