iio: hid-sensor-hub: Remove hard coded indexes

Remove the hard coded indexes, instead search for usage id and
use the index to set the power and report state.
This will fix issue, where the report descriptor doesn't contain
the full list of possible selector for power and report state.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>