Fixed data decoding for PmodMAXSONAR driver
Fixed data decoding for PmodMAXSONAR driver

The pattern for matching the data returned by the pmod is
wrong. According to the reference manual (https://reference.digilentinc.com/_media/reference/pmod/pmodmaxsonar/pmodmaxsonar_rm.pdf) there is only one 'R'-character in front of the sent distance.

I tested this fix during a GRiSP tutorial session on 06.12.2018:
 - old behavior was that 'undefined' was returned
 - new behavior is that reasonable distances (in inch) are returned


grisp/grisp,grisp/grisp