Address Coverity warnings in keymgr.c

Address Coverity warnings in keymgr.c

Coverity showed that the return value of `dst_key_gettime` was
unchecked in INITIALIZE_STATE. If DST_TIME_CREATED was not set we
would set the state to be initialized to a weird last changed time.

This would normally not happen because DST_TIME_CREATED is always
set. However, we would rather set the time to now (as the comment
also indicates) not match the creation time.

The comment on INITIALIZE_STATE also needs updating as we no
longer always initialize to HIDDEN.