xfs: fix typo in comment of xfs_dinode_t.

There should be "XFS_DFORK_DPTR, XFS_DFORK_APTR, and XFS_DFORK_PTR" instead
of "XFS_DFORK_PTR, XFS_DFORK_DPTR, and XFS_DFORK_PTR".
Signed-off-by: NChen Baozi <baozich@gmail.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

fs/xfs/xfs_dinode.h

@@ -33,7 +33,7 @@ typedef struct xfs_timestamp {
  * variable size the leftover area split into a data and an attribute fork.
  * The format of the data and attribute fork depends on the format of the
  * inode as indicated by di_format and di_aformat.  To access the data and
- * attribute use the XFS_DFORK_PTR, XFS_DFORK_DPTR, and XFS_DFORK_PTR macros
+ * attribute use the XFS_DFORK_DPTR, XFS_DFORK_APTR, and XFS_DFORK_PTR macros
  * below.
  *
  * There is a very similar struct icdinode in xfs_inode which matches the