inetutils: add --with-libreadline-prefix to avoid host contamination

Fix the do_rootfs error:
| Computing transaction...error: Can't install inetutils-telnetd-1.9.1-r1.1@i686: no package provides libreadline.so.5

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Joe MacDonald <joe@deserted.net>