hw/riscv: opentitan: Fixup resetvec

hw/riscv: opentitan: Fixup resetvec

The resetvec for the OpenTitan machine ended up being set to an out of
date value, so let's fix that and bump it to the correct start address
(after the boot ROM)

Fixes: bf8803c64d75 "hw/riscv: opentitan: bump opentitan version"
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220914101108.82571-3-alistair.francis@wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>