[dv/csrng_agent] Only increment the count if the ack is sent
[dv/csrng_agent] Only increment the count if the ack is sent

This PR moves the timing to increment counters.
Currently the counter will increment when we see the gen request.
With this change, will only increment the count if the `ack` is sent.
This will eliminate the case where reset is issued.

Signed-off-by: Cindy Chen <399ad771a111eac8923348b1e2af093034e5d4f1@opentitan.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan