mtd locking fix and cleanups

[Christoph Hellwig]

Hi mtd maintainers,

the first series in this patch fixes a lock order reversal reported by
Guenter based on a recent commit, although from code inspection it should
have been around for much longer.

The rest is drive-by cleanups in the area that I noticed while trying to
understand the locking changes.  These are untested and need to be handled
with care!

Diffstat:
 ftl.c         |    2 -
 mtd_blkdevs.c |   60 ++++++----------------------------------------------------
 rfd_ftl.c     |    2 -
 3 files changed, 9 insertions(+), 55 deletions(-)