staging: iio: tsl2583: remove redundant power_state sysfs attribute

IIO devices have a /sys/bus/iio/devices/iio:deviceX/power/ directory
that allows viewing and controling various power parameters. The tsl2583
driver also has an additional custom sysfs attribute named power_state
that is not needed. This patch removes the redundant power_state sysfs
attribute.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>