vsftpd: correct openssl linking after 1d046a5c (vsftpd: use pkg-config to get OpenSSL link flags)

Fixes:
http://autobuild.buildroot.net/results/221/221c987a9657caefad54bcc2fe9d2d71189c94c5/
http://autobuild.buildroot.net/results/90c/90cea7c4fdb3e5af923eedf96d79594d6d02e563/



vsftpd directly uses symbols from libcrypto (X509_{digest,free}), so it
needs to link against both.

This doesn't trigger for static builds as libssl internally uses libcrypto
(and lists it in Requires.private).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>