arm64: microbench: get correct ipi received num

If ipi_exec() fails because of timeout, we shouldn't increase
the number of ipi received.

Signed-off-by: Jingyi Wang <wangjingyi11@huawei.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>