Then we can use it instead of magic number 1.
Reviewed-by: NHidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: NSheng Yang <sheng@linux.intel.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>