Merge tag 'md/3.18-fix' of git://neil.brown.name/md

Pull md bugfix from Neil Brown:
 "One fix for md for 3.18.

  This fixes a regression introduced in 3.13"

* tag 'md/3.18-fix' of git://neil.brown.name/md:
  md: Always set RECOVERY_NEEDED when clearing RECOVERY_FROZEN