CLEANUP: Fix spelling errors in comments

This is from the output of codespell. It's done at once over a bunch
of files and only affects comments, so there is nothing user-visible.
No backport needed.
diff --git a/include/import/ebmbtree.h b/include/import/ebmbtree.h
index a010624..23ef554 100644
--- a/include/import/ebmbtree.h
+++ b/include/import/ebmbtree.h
@@ -465,7 +465,7 @@
 	}
 
  not_found:
-	/* Walk down last cover tre if it exists. It does not matter if cover is NULL */
+	/* Walk down last cover tree if it exists. It does not matter if cover is NULL */
 	return ebmb_entry(eb_walk_down(cover, EB_LEFT), struct ebmb_node, node);
 }