x86/hpet: fix cpumask allocation after 23990:1c8789852eaf

x86/hpet: fix cpumask allocation after 23990:1c8789852eaf

hpet_fsb_cap_lookup(), if it doesn't find any FSB capable timer,
leaves hpet_events allocated, while hpet_events->cpumask may not have
been, As we're pretty generous with these one-time allocations already
(in that hpet_events doesn't get freed when no usable counters were
found, even if in that case only the first array entry [or none at
all] may get used), simply make the cpumask allocation in the legacy
case independent of whether hpet_events was NULL before.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Christoph Egger <Christoph.Egger@amd.com>
Acked-by: Christoph Egger <Christoph.Egger@amd.com>
Committed-by: Keir Fraser <keir@xen.org>