KVM: PPC: Book3S HV: Increase timeout for grabbing secondary threads

Occasional failures have been seen with split-core mode and migration
where the message "KVM: couldn't grab cpu" appears.  This increases
the length of time that we wait from 1ms to 10ms, which seems to
work around the issue.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>