doc(hmac): Update Error section
doc(hmac): Update Error section

In previous document, **Interrupt Handling** section was empty. In this
commit, the section is revised to **Error** and lists out the type of
errors SW may receive from HMAC.

Signed-off-by: Eunchan Kim <cb7bc7ceb22698f298c67faa994fd9ddf3cab298@opentitan.org>

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