staging: iio: tsl2x7x: move integration_time* attributes to IIO_INTENSITY channel

The integration_time* attributes are currently associated with the
IIO_LIGHT channel but should be associated with the IIO_INTENSITY
channel. Directory listing of the sysfs attributes for a TSL2772
with this patch applied:

dev
events
in_illuminance0_calibrate
in_illuminance0_calibscale_available
in_illuminance0_input
in_illuminance0_lux_table
in_illuminance0_target_input
in_intensity0_calibbias
in_intensity0_calibscale
in_intensity0_integration_time
in_intensity0_integration_time_available
in_intensity0_raw
in_intensity1_raw
in_proximity0_calibrate
in_proximity0_calibscale
in_proximity0_calibscale_available
in_proximity0_raw
name
of_node
power
subsystem
uevent

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>