fs/ntfs3: make ntfs_writeback_ops static

Fix below sparse warnings:
fs/ntfs3/inode.c:972:34: sparse: sparse: symbol 'ntfs_writeback_ops' was not declared.
Should it be static?

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601061424.nbKLNwC5-lkp@intel.com/
Signed-off-by: sunliming <sunliming@kylinos.cn>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: sunliming

fs/ntfs3/inode.c

@@ -969,7 +969,7 @@ static ssize_t ntfs_writeback_range(struct iomap_writepage_ctx *wpc,
 }
 
 
-const struct iomap_writeback_ops ntfs_writeback_ops = {
+static const struct iomap_writeback_ops ntfs_writeback_ops = {
 	.writeback_range = ntfs_writeback_range,
 	.writeback_submit = iomap_ioend_writeback_submit,
 };