ntfs: Fix up mm merge

/tmp/next/build/fs/ntfs/file.c: In function 'ntfs_file_mmap_prepare':
/tmp/next/build/fs/ntfs/file.c:657:13: error: implicit declaration of function 'vma_desc_test_flags'; did you mean 'vma_desc_set_flags'? [-Wimplicit-function-declaration]
  657 |         if (vma_desc_test_flags(desc, VMA_WRITE_BIT)) {
      |             ^~~~~~~~~~~~~~~~~~~

Signed-off-by: Mark Brown <broonie@kernel.org>