btrfs: use new dedupe data function pointer

Now that the VFS encapsulates the dedupe ioctl, wire up btrfs to it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/btrfs/ctree.h

@@ -4024,6 +4024,8 @@ void btrfs_get_block_group_info(struct list_head *groups_list,
 				struct btrfs_ioctl_space_info *space);
 void update_ioctl_balance_args(struct btrfs_fs_info *fs_info, int lock,
 			       struct btrfs_ioctl_balance_args *bargs);
+ssize_t btrfs_dedupe_file_range(struct file *src_file, u64 loff, u64 olen,
+			   struct file *dst_file, u64 dst_loff);
 
 /* file.c */
 int btrfs_auto_defrag_init(void);