commit 70dddeee upstream.

If the in-kernel push interface is used we may have a different masks
on the device buffer and the kernel buffer and in this case the device
should generate data for the reunion of the buffers, which is
available at indio_dev->active_scan_mask.

Compiled tested only except for bmc150-accel which was tested at
runtime with the hardware.
Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[ luis: backported to 3.16: dropped changes to:
  - drivers/iio/accel/bmc150-accel.c
  - drivers/iio/accel/kxcjk-1013.c
  - drivers/iio/gyro/bmg160.c
  - drivers/iio/imu/kmx61.c
  - drivers/iio/proximity/sx9500.c ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>