iio:light:stk3310: use correct names and type for state

Indicate the bit number of predefined states, make use of these names and
change the state type in _resume to u8 to avoid type casting.

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Reviewed-by: Tiberiu Breana <tiberiu.a.breana@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>