consensus/ethash: fixed typo (ethereum#16665)

consensus/ethash/ethash.go

@@ -156,7 +156,7 @@ type lru struct {
 	futureItem interface{}
 }
 
-// newlru create a new least-recently-used cache for ither the verification caches
+// newlru create a new least-recently-used cache for either the verification caches
 // or the mining datasets.
 func newlru(what string, maxItems int, new func(epoch uint64) interface{}) *lru {
 	if maxItems <= 0 {