ipa: raspberrypi: histogram: Add a constructor for an empty histogram

Add a default constructor to the RPiController::Histogram class that creates
an empty histogram. Since this is a cumulative histogram, push a value of 0 into
the first (and only) bin to signify this.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/raspberrypi/controller/histogram.h

@@ -20,6 +20,11 @@ namespace RPiController {
 class Histogram
 {
 public:
+	Histogram()
+	{
+		cumulative_.push_back(0);
+	}
+
 	template<typename T> Histogram(T *histogram, int num)
 	{
 		assert(num);