Unbreak makefs -t cd9660 after r289687

buffer_head needs to be freed -- not buffer

Detected by jemalloc, i.e. running makefs failed the arena assert
because my copy of malloc on CURRENT is compiled with the default
!MALLOC_PRODUCTION asserts on

Pointyhat to: ngie
PR: 203647
X-MFC with: r289687
Sponsored by: EMC / Isilon Storage Division

usr.sbin/makefs/cd9660/cd9660_write.c

@@ -215,7 +215,7 @@ cd9660_write_path_table(FILE *fd, off_t sector, int mode)
 
 	ret = cd9660_write_filedata(fd, sector, buffer_head,
 	    path_table_sectors);
-	free(buffer);
+	free(buffer_head);
 	return ret;
 }