KVM: Wake up waitqueue before calling get_cpu()

This moves the get_cpu() call down to be called after we wake up the
waiters. Therefore the waitqueue locks can safely be rt mutex.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Sven-Thorsten Dietrich <sven@thebigcorporation.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>