Fix time accounting on msp430 Series 5 MCU based platforms (wismote)
Fix time accounting on msp430 Series 5 MCU based platforms (wismote)

See https://github.com/contiki-os/contiki/pull/727 for explanation

bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,arurke/contiki,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr