treewide: Remove top-level const from return types

Top-level `const` qualifiers are not useful, so avoid them. This is done
either by simply removing the top-level `const`, or making the function
return a reference to const where that is appropriate.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>

src/ipa/libipa/histogram.h

@@ -36,7 +36,7 @@ public:
 	}
 
 	size_t bins() const { return cumulative_.size() - 1; }
-	const Span<const uint64_t> data() const { return cumulative_; }
+	Span<const uint64_t> data() const { return cumulative_; }
 	uint64_t total() const { return cumulative_[cumulative_.size() - 1]; }
 	uint64_t cumulativeFrequency(double bin) const;
 	double quantile(double q, uint32_t first = 0, uint32_t last = UINT_MAX) const;