Fix the panic message of MemQuota.Record (#10479)

close #10478

cdc/processor/memquota/mem_quota.go

@@ -172,9 +172,12 @@ func (m *MemQuota) Record(span tablepb.Span, resolved model.ResolvedTs, nBytes u
 		// Can't find the table record, the table must be removed.
 		usedBytes := m.usedBytes.Load()
 		if usedBytes < nBytes {
-			log.Panic("MemQuota.refund fail",
-				zap.Uint64("used", usedBytes), zap.Uint64("refund", nBytes))
+			log.Panic("MemQuota.record fail",
+				zap.Uint64("used", usedBytes), zap.Uint64("record", nBytes))
 		}
+		// If we cannot find the table, then the previous acquired memory quota needed to be returned.
+		// Note that "usedBytes.Add(^(nBytes - 1))" means "usedBytes.Sub(nBytes)". But atomic don't
+		// have Sub method.
 		if m.usedBytes.Add(^(nBytes - 1)) < m.totalBytes {
 			m.blockAcquireCond.Broadcast()
 		}