lavf/libssh: call ssh_userauth_none before ssh_userauth_list

According to doc, ssh_userauth_none must be called before ssh_userauth_list.
It solves login issue for new versions of libssh.

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>