mdadm: Update to version 4.2

mdadm: Update to version 4.2

- Update from 4.1 to 4.2
- Update of rootfile not required
- Changelog is no longer updated. The package directs you to the git commits to find
   the changes. https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/log/
- Announcement of update says-
   The release includes more than two years of development and bugfixes,
    so it is difficult to remember everything. Highlights include
    enhancements and bug fixes including for IMSM RAID, Partial Parity
    Log, clustered RAID support, improved testing, and gcc-9 support.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Peter Müller <peter.mueller@ipfire.org>