The function actually returns monotonic time value in nanosecond,
the "ticks" is not suitable.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc  Peter Crosthwaite <crosthwaite.peter@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Message-Id: <1469790338-28990-3-git-send-email-caoj.fnst@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>