c++: Very minor change in range() method

Change the type of the cRange variable from 'comedi_range *' to 'const
comedi_range *'.  This holds the return value of the method which is
already of type 'const comedi_range *'.

c++/include/comedilib.hpp

@@ -846,7 +846,7 @@ namespace comedi
 		}
 		const comedi_range* range(unsigned channel, unsigned range_index) const
 		{
-			comedi_range *cRange = comedi_get_range(comedi_handle(), index(), channel, range_index);
+			const comedi_range *cRange = comedi_get_range(comedi_handle(), index(), channel, range_index);
 			if(cRange == 0)
 			{
 				std::ostringstream message;