ecdh: Fix a memory leak in ecdh_build_k().
ecdh: Fix a memory leak in ecdh_build_k().

Thanks to Tom Judge for the report.

kedazo/libssh,Distrotech/libssh,DouglasHeriot/libssh,sebadoom/libssh,wangshawn/libssh,Distrotech/libssh,mwgoldsmith/libssh,kedazo/libssh,wangshawn/libssh,sebadoom/libssh,mwgoldsmith/ssh,robxu9/libssh,mwgoldsmith/libssh,sebadoom/libssh,jt1/honeypot-libssh,nviennot/libssh,pouete/libssh,nviennot/libssh,pouete/libssh,mwgoldsmith/libssh,DouglasHeriot/libssh,nviennot/libssh,kedazo/libssh,taikoo/libssh,pouete/libssh,robxu9/libssh,elastichosts/libssh,elastichosts/libssh,mwgoldsmith/ssh,DouglasHeriot/libssh,nviennot/libssh,taikoo/libssh,sebadoom/libssh,Distrotech/libssh,jt1/honeypot-libssh,bigcat26/libssh-mod,robxu9/libssh,taikoo/libssh,robxu9/libssh,bigcat26/libssh-mod,Distrotech/libssh,wangshawn/libssh,taikoo/libssh,mwgoldsmith/ssh,pouete/libssh,elastichosts/libssh,bigcat26/libssh-mod,DouglasHeriot/libssh,jt1/honeypot-libssh,bigcat26/libssh-mod,kedazo/libssh,jt1/honeypot-libssh,wangshawn/libssh,mwgoldsmith/libssh,mwgoldsmith/ssh