[util/dvsim] Fix confusing error message
[util/dvsim] Fix confusing error message

The error emitted when there are circular includes is confusing, making
diagnosis more difficult.

Signed-off-by: Guillermo Maturana <085716c7110d3f31793f7d964c2e5fd26da1c550@google.com>

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