[mlir][Vector] Avoid infinite loop in InnerOuterDimReductionConversion.

This patterns tries to convert an inner (outer) dim reduction to an
outer (inner) dim reduction. Doing this on a 1D or 0D vector results
in an infinite loop since the converted op is same as the original
operation. Just returning failure when source rank <= 1 fixes the
issue.

Differential Revision: https://reviews.llvm.org/D115426

mlir/lib/Dialect/Vector/VectorMultiDimReductionTransforms.cpp

@@ -41,6 +41,9 @@ public:
     auto src = multiReductionOp.source();
     auto loc = multiReductionOp.getLoc();
     auto srcRank = multiReductionOp.getSourceVectorType().getRank();
+    // If the rank is less than or equal to 1, there is nothing to do.
+    if (srcRank <= 1)
+      return failure();
 
     // Separate reduction and parallel dims
     auto reductionDimsRange =