uuid: fix incorrect uuid_equal conversion in test_uuid_test

Fixes: df33767d

 ("uuid: hoist helpers uuid_equal() and uuid_copy() from xfs")
Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>