commit bba6d9e4 upstream.

When system bootup without get sensor property, set sensor
property will be fail.

If no get_feature operation done before set_feature, the sensor
properties will all be the initialized value, which is not the
same with sensor real properties. When set sensor property it will
write back to sensor the changed perperty data combines with other
sensor properties data, it is not right and may be dangerous.

In order to get all sensor properties, choose to read one of the sensor
properties(no matter read any sensor peroperty, driver will get all
the peroperties and return the requested one).

Fixes: 73c6768b ("iio: hid-sensors: Common attribute and trigger")
Signed-off-by: Song Hongyan <hongyan.song@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[bwh: Backported to 3.16:
 - sensor_hub_get_feature() doesn't take a 'buffer_size' parameter
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>