[dv/alert_esc_agent] Use mon_cb's signal in alert_monitor
[dv/alert_esc_agent] Use mon_cb's signal in alert_monitor

This PR fixes alert_monitor - it directly uses cfg.vif.alert_* signals
instead of the signals from the clocking block. Because of this, there
is a hard-coded one cycle delay in alert_monitor.
Thanks @weicaiyang for pointing that out during a review.

Signed-off-by: Cindy Chen <399ad771a111eac8923348b1e2af093034e5d4f1@google.com>

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