tn5250: fix openssl dir

If openssl devfiles are installed in the host the automatic lookup might
find that and cause issues.
So be explicit on the directory to avoid a search and patch the
directory logic since it's got a bug. Fixes:
http://autobuild.buildroot.net/results/5dd/5ddc8636d6555851f692c0c21f583df235340b19/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>