iio: fix drivers that check buffer->scan_mask

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>