[mlir] feat(vector): drop unit dims from memrefs for xfer_read/write for non… (PR #187076)

[Andrzej Warzyński]

================
@@ -532,12 +532,15 @@ class TransferReadDropUnitDimsPattern
       }
       FailureOr<Value> rankReducedCreateMask =
           createMaskDropNonScalableUnitDims(rewriter, loc, createMaskOp);
-      if (failed(rankReducedCreateMask)) {
+      if (succeeded(rankReducedCreateMask)) {
+        maskOp = *rankReducedCreateMask;
+        LDBG() << "  -> Successfully reduced mask dimensions";
+      } else if (createMaskOp.getVectorType().getRank() !=
+                 reducedVectorType.getRank()) {
+        // Mask needs reduction but couldn't be reduced.
         LDBG() << "  -> Failed to reduce mask dimensions";
----------------
banach-space wrote:

```suggestion
        LDBG() << "  -> Mask reduction required, but failed";
```

https://github.com/llvm/llvm-project/pull/187076