doc/funcref: Fix "Returns:" for comedi_to_physical.
doc/funcref: Fix "Returns:" for comedi_to_physical.

There was a stray space before the "Returns:" heading so it wasn't
processed as intended.  Also, there was an empty line above it leading
to an empty paragraph in the DocBook funcref.xml.

olsonse/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,olsonse/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,Linux-Comedi/comedilib