[mlir][sparse] fixed typo

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorStorageLayout.h

public:
   RankedTensorType getTensorType() const { return rType; }
   ValueArrayRef getFields() const { return fields; }
 
 protected:
   RankedTensorType rType;
   ValueArrayRef fields;
 };
 
-/// Uses ValueRange for immuatable descriptors;
+/// Uses ValueRange for immutable descriptors.
 class SparseTensorDescriptor : public SparseTensorDescriptorImpl<ValueRange> {
 public:
   SparseTensorDescriptor(Type tp, ValueRange buffers)
       : SparseTensorDescriptorImpl<ValueRange>(tp, buffers) {}
 
   Value getIdxMemRefOrView(OpBuilder &builder, Location loc,
                            unsigned idxDim) const;
 };