staging: iio: tsl2583: change current chip state from a tristate to a bool

The current chip state is represented as a tristate (working, suspended,
and unknown). The unknown state was not used. This patch changes the
chip state so that it is now represented as a single boolean value
(suspended).

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