[prim] Fix DC sythesis error
[prim] Fix DC sythesis error

DC doesn't allow hierachy path reference, like
`assign PRIM_HIER_.unused_assert_connected = 1'b1;`

Signed-off-by: Weicai Yang <4fa8c7762ee4da95e3dee7dae2c3263ea16637f9@google.com>

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