Fixes issue #900 KC_PWR not working

[wilba]

This fixes #900 which was broken with the fix for #522.

I've limited the "usage" range to the only three "usage" codes in the source. The data being sent needs to be a 1-based index to the "array" of states, hence the "logical" min/max of 1..3.

Well, that's how I'm interpreting the HID spec: http://www.usb.org/developers/hidpage/HID1_11.pdf page 32:

The value returned by an Array item is an index so it is recommended that:

1. An Array field returns a 0 value when no controls in the array are asserted.
2. The Logical Minimum equals 1.
3. The Logical Maximum equal the number of elements in the array.

[jackhumbert]

Awesome - good catch :)