Fix typo in commit 6f7d02aa

Per pink buildfarm.

src/backend/executor/instrument.c

@@ -63,7 +63,7 @@ void
 InstrStartNode(Instrumentation *instr)
 {
 	if (instr->need_timer &&
-		INSTR_TIME_SET_CURRENT_LAZY(instr->starttime))
+		!INSTR_TIME_SET_CURRENT_LAZY(instr->starttime))
 		elog(ERROR, "InstrStartNode called twice in a row");
 
 	/* save buffer usage totals at node entry, if needed */