32 should better be replaced by "symbolFactor" (#9203)

Signed-off-by: tanghengjian <1040104807@qq.com>

tsdb/index/index.go

@@ -1180,7 +1180,7 @@ func newReader(b ByteSlice, c io.Closer) (*Reader, error) {
 				lastKey = nil
 				valueCount = 0
 			}
-			if valueCount%32 == 0 {
+			if valueCount%symbolFactor == 0 {
 				r.postings[key[0]] = append(r.postings[key[0]], postingOffset{value: key[1], off: off})
 				lastKey = nil
 			} else {
@@ -1335,7 +1335,7 @@ func (s Symbols) ReverseLookup(sym string) (uint32, error) {
 		i--
 	}
 	d.Skip(s.offsets[i])
-	res := i * 32
+	res := i * symbolFactor
 	var lastLen int
 	var lastSymbol string
 	for d.Err() == nil && res <= s.seen {