xfs: xfs_buf_write_fail_rl_state can be static

Fix sparse warning introduced by commit ac8809f9 ("xfs: abort
metadata writeback on permanent errors").
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

fs/xfs/xfs_buf_item.c

@@ -501,7 +501,7 @@ xfs_buf_item_unpin(
  * buffer being bad..
  */
 
-DEFINE_RATELIMIT_STATE(xfs_buf_write_fail_rl_state, 30 * HZ, 10);
+static DEFINE_RATELIMIT_STATE(xfs_buf_write_fail_rl_state, 30 * HZ, 10);
 
 STATIC uint
 xfs_buf_item_push(