sde-create-iso: hopefully got arithmetics right this time

bin/sde-create-iso

@@ -83,9 +83,9 @@ fmtsize()
 	else
 		lsrings=$( echo $strings | tr "[:upper:]" "[:lower:]" )
 		case "$lstrings" in
-			k|kb|kib|kylobytes|kilobites)	media_size="$numbers"/1024 ;;
+			k|kb|kib|kylobytes|kilobites)	let media_size="$numbers"/1024 ;;
 			m|mb|mib|megabytes|megabites)	media_size="$numbers" ;;
-			g|gb|gib|gigabytes|gigabites)	media_size="$numbers"*1024 ;;
+			g|gb|gib|gigabytes|gigabites)	let media_size="$numbers"*1024 ;;
 			                           *)	echo_abort 1 "$strings: Unknown size unit specified, aborting."
 		esac
 	fi