xfs: const-ify xfs_owner_info arguments

Only certain functions actually change the contents of an
xfs_owner_info; the rest can accept a const struct pointer.  This will
enable us to save stack space by hoisting static owner info types to
be const global variables.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -536,7 +536,7 @@ __xfs_bmap_add_free(
 	struct xfs_trans		*tp,
 	xfs_fsblock_t			bno,
 	xfs_filblks_t			len,
-	struct xfs_owner_info		*oinfo,
+	const struct xfs_owner_info	*oinfo,
 	bool				skip_discard)
 {
 	struct xfs_extent_free_item	*new;		/* new element */