Return value should be zero for success. This was forgotten for timestamp
feature. Verified on RealSense cameras.

Fixes: a96cd0f9 ("iio: accel: hid-sensor-accel-3d: Add timestamp")
Signed-off-by: Dmitry Perchanov <dmitry.perchanov@intel.com>
Link: https://lore.kernel.org/r/a6dc426498221c81fa71045b41adf782ebd42136.camel@intel.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>