iio: nitpicking on sysfs-bus-iio

v2: address comments by Jonathan Cameron
* add more output power down modes
* spelling of etc.

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>