power: implement asmilliwatts for sized arrays

src/power.rs

@@ -25,6 +25,13 @@ impl<T> AsMilliwatts for [T] where T: AsMilliwatts {
     }
 }
 
+
+impl<T, const S: usize> AsMilliwatts for [T; S] where T: AsMilliwatts {
+    fn as_milliwatts(&self) -> u32 {
+        self.iter().map(|p| { p.as_milliwatts() }).sum()
+    }
+}
+
 pub fn brightness_for_mw(total_mw : u32, target : u8, max_power: u32) -> u8 {
     let target32 = target as u32;
     let requested_mw = (total_mw * target32) / 256;