[PIPELINE] Turning pipeliner error into warning, explaining that pipelining is disabled (triton-lang#5867)

Author: pawelszczerbuk

lib/Dialect/TritonGPU/Transforms/Pipeliner/PipelineExpander.cpp

@@ -259,7 +259,8 @@ bool LoopPipelinerInternal::verifySchedule() {
       int64_t producerCycle = it->second;
       if (consumerCycle < producerCycle - numCylesPerIter * distance) {
         InFlightDiagnostic diag =
-            consumer->emitError("operation scheduled before its operands");
+            consumer->emitWarning("operation scheduled before its operands. "
+                                  "Pipelining will be disabled.");
         diag.attachNote(producer->getLoc())
             .append("operand defined here: ")
             .appendOp(*producer, OpPrintingFlags().printGenericOpForm());