Permit the creation of just cd0 if desired. Previously it always

created cd1 as well due to an off-by-one error left over from
revision 1.249.

PR:		conf/20436
Submitted by:	Andre Albsmeier <andre.albsmeier@mchp.siemens.de>
MFC after:	1 week

etc/MAKEDEV

@@ -831,7 +831,7 @@ acd*|cd*|mcd*|scd*)
 	scd*) units=`expr $i : '...\(.*\)'`; name=scd; chr=45;;
 	esac
 	if [ -z "${units}" -o "${units}" -le 0 ]; then
-		units=1
+		units=0
 	fi
 	if [ "${units}" -le 31 ]; then
 		i=0