Merge tag 'header_cleanup-2024-01-20' of https://evilpiepirate.org/git/bcachefs

Pull header fix from Kent Overstreet:
 "Just one small fixup for the RT build"

* tag 'header_cleanup-2024-01-20' of https://evilpiepirate.org/git/bcachefs:
  spinlock: Fix failing build for PREEMPT_RT