Fixed error when FDISK in check_mmc() returns multiple matches.

mk_mmc.sh

@@ -1268,7 +1268,7 @@ populate_boot () {
 }
 
 check_mmc () {
-	FDISK=$(LC_ALL=C fdisk -l 2>/dev/null | grep "Disk ${media}" | awk '{print $2}')
+	FDISK=$(LC_ALL=C fdisk -l 2>/dev/null | grep "Disk ${media}[^(a-z,A-Z,0-9)]" | awk '{print $2}')
 
 	if [ "x${FDISK}" = "x${media}:" ] ; then
 		echo ""