The authors would like to clarify that [1] is the original source of a Figure that was included in our previously published manuscript as Figure 7 [2]. Although a reference to [1] was provided in [2], a direct reference was not inserted in the image caption. The image is reshown here as Figure 1 for convenience. We would like to thank Dr E. Klintström, the copyright holder, for agreeing to the reuse of the Figure.