z1 msp430_sync_dco not working in mspsim, working on H/W

[simonduq]

The new implementation of msp430_sync_dco from the following contiki-os/contiki commit:
contiki-os/contiki@68b65e6
works on z1 H/W nodes but not mspsim. Hardware timers (both A and B) go twice as slow as intended. For example, time_seconds() is equal to half the number of seconds elapsed since startup.