[arch-general] mdadm segfaults with kernel 2.6.38.2

[Norbert Zeh]

Upstream is aware of the issue, which occurs with version 0.90 md
arrays.  The latest git version fixes the problem.  So it's only a
matter of waiting for a new release version from upstream for this to
trickle into the arch repos.  For now I simply keep mdadm pinned on
v3.1.5, which is in fact the version currently recommended by upstream
unless you need the features introduced in 3.2.1.

- Norbert