owners: add Audra as memory management reviwer and fix list

Add Audra Mitchell as MM reviewer.

For some reason mm-maint@redhat.com was listed as mailing list under
memory controller drivers, probably a mistake since the proper memory
management entry is missing a mailing list. Relocate it accordingly.

Cc: aubaker@redhat.com
Cc: raquini@redhat.com
Cc: dledford@redhat.com
Cc: prarit@redhat.com
Signed-off-by: Aristeu Rozanski arozansk@redhat.com