[mlir] Fix warnings

This patch fixes:

  mlir/include/mlir/ExecutionEngine/SparseTensor/Storage.h:955:20:
  error: unused variable 'sz' [-Werror,-Wunused-variable]

  mlir/lib/Dialect/Linalg/TransformOps/LinalgTransformOps.cpp:1460:2:
  error: extra ';' outside of a function is incompatible with C++98
  [-Werror,-Wc++98-compat-extra-semi]