[mlir][vector] Restore assert and fix typos (#68581)

Follow-up for #68400 - restoring an assert that was accidentally removed
and fixed a typo in a diagnostic.

Author: banach-space

mlir/lib/Dialect/Vector/Transforms/LowerVectorContract.cpp

@@ -432,6 +432,9 @@ struct UnrolledOuterProductGenerator
       return failure();
 
     int reductionSize = lhsType.getDimSize(reductionDim);
+    assert(reductionSize > 0 &&
+           "Reduction dim must be a known static size to allow unrolling");
+
     // Incremental support for masking.
     if (mask && !maybeMask.has_value())
       return failure();
@@ -997,15 +1000,15 @@ FailureOr<Value> ContractionOpLowering::lowerParallel(PatternRewriter &rewriter,
       });
     if (lhsType.getScalableDims()[lhsIndex])
       return rewriter.notifyMatchFailure(op, [&](Diagnostic &diag) {
-        diag << "Unrolloing scalable dimension (lhsIndex=" << lhsIndex
+        diag << "Unrolling scalable dimension (lhsIndex=" << lhsIndex
              << ") is not supported yet";
       });
     dimSize = lhsType.getDimSize(lhsIndex);
   } else if (rhsIndex >= 0) {
     iterIndex = iMap[1].getDimPosition(rhsIndex);
     if (rhsType.getScalableDims()[rhsIndex])
       return rewriter.notifyMatchFailure(op, [&](Diagnostic &diag) {
-        diag << "Unrolloing scalable dimension (lhsIndex=" << lhsIndex
+        diag << "Unrolling scalable dimension (rhsIndex=" << rhsIndex
              << ") is not supported yet";
       });
     dimSize = rhsType.getDimSize(rhsIndex);