mdadm: force a uuid swap on big endian

mdadm: force a uuid swap on big endian

The code path for metadata 0.90 calls a common routine
fname_from_uuid that uses metadata 1.2. The code expects member
swapuuid to be setup and usable. But it is only setup when using
metadata 1.2. Since the metadata 0.90 did not create swapuuid
and set it. The test (st->ss == &super1) ? 1 : st->ss->swapuuid
fails. The swapuuid is set at compile time based on byte order.
Any call based on metadata 0.90 and on big endian processors,
the --export uuid will be incorrect.

Signed-Off-by: Nigel Croxon <ncroxon@redhat.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>