ATLEDGE-572: Fix getStepDetectionMode()
ATLEDGE-572: Fix getStepDetectionMode()

This function is reading all 8 bits of RA_STEP_CONF_1 (0x7A-0x7B)
to obtain a value for min_step_buf, though this value is only
represented by the lower 3 bits; bit 4 is used as the 'enable' bit.
As a consequence, this function will read the step detection mode
incorrectly when step counting is enabled. Fix this by only reading
the lower 3 bits of RA_STEP_CONF_1.

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