"Way" is probably one of the oldest English words for road or path, and of course a barleyfield would have one running through it. But is it possible Winwood sings "wain," an archaic term for wagon (two lines later, for rhyming reasons, a "cart")? In fact an answer to this question would hinge on is just how "traditional" the song is in this form. The song is old, but the only other / older version I know is the Robert Burns version and it is very different and does not contain this line though it is much longer. If Capaldi/Winwood were rewriting Burns' version, it seems unlikely they would insert a new archaism (unless it helped rhyming, I guess). But other phrases are also a bit archaic --"serving him most barbarously"-- that do not appear in Burns (though the line "the miller has served him worse than that" is). Either way (!), it's a slightly odd line. If there is another version somewhere it might hold an answer. Another possibility is "pale and drawn" rather than "pale and wan," though the Burns version has "wan and pale."