raid5 bio handling cleanups

[Christoph Hellwig]

Hi Song,

this series cleans up the raid5 bio handling to take advantage of
the bio allocation interface changes in Jens' for-5.18 branches.

Diffstat:
 raid5-cache.c |   33 ++++++++++++++++-----------------
 raid5-ppl.c   |    5 ++---
 raid5.c       |   25 ++++++++-----------------
 3 files changed, 26 insertions(+), 37 deletions(-)