xfs: constify the name argument to various directory functions

Various directory functions do not modify their @name parameter,
so mark it const to make that clear.  This will enable us to mark
the global xfs_name_dotdot variable as const to prevent mischief.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/xfs_inode.c

@@ -658,9 +658,9 @@ xfs_ip2xflags(
  */
 int
 xfs_lookup(
-	xfs_inode_t		*dp,
-	struct xfs_name		*name,
-	xfs_inode_t		**ipp,
+	struct xfs_inode	*dp,
+	const struct xfs_name	*name,
+	struct xfs_inode	**ipp,
 	struct xfs_name		*ci_name)
 {
 	xfs_ino_t		inum;