imu: fixed error in reg_write_bits
imu: fixed error in reg_write_bits

- reg_write_bits was erroneously clearing all other bits in
  a register outside of the bits targeted for the write
  operation.

Signed-off-by: Dan O'Donovan <2591e5f46f28d303f9dc027d475a5c60d8dea17a@emutex.com>

bigdinotech/corelibs-arduino101,SidLeung/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,sgbihu/corelibs-arduino101,01org/corelibs-arduino101,eriknyquist/corelibs-arduino101,sgbihu/corelibs-arduino101,linrjing/corelibs-arduino101,facchinm/corelibs-arduino101,linrjing/corelibs-arduino101,bigdinotech/corelibs-arduino101,01org/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,facchinm/corelibs-arduino101,SidLeung/corelibs-arduino101,sandeepmistry/corelibs-arduino101,bigdinotech/corelibs-arduino101,eriknyquist/corelibs-arduino101,sgbihu/corelibs-arduino101,01org/corelibs-arduino101,yashaswini-hanji/corelibs-arduino101,sandeepmistry/corelibs-arduino101,sandeepmistry/corelibs-arduino101