STPK-1429 Support floating point sampling rates

STPK-1429 Support floating point sampling rates

The Kionix accelerometer found on the MRD 7 advertises
support for 6.25 and 12.5 Hz, so open up a little the
scope of what we consider a valid sampling rate.

Some %f specifications were replaced by %g because %f
shows zero digits in the style of 3.140000, and some
sysfs writes would not be accepted because of this format.

Issue: STPK-1429

Change-Id: I35379aec4d3f03bfdf27a17d192ebc0dfbef3441
Signed-off-by: Patrick Porlan <patrick.porlan@intel.com>