package/autossh: really fix the path to ssh

The ./configure script is not up-to-date with what is in configure.ac,
which prevents --with-ssh from working properly.

So, we autoreconfigure autossh, which fixes the issue.

Note however that this is not really an autotools package, since it only
uses autoconf and not automake. However, making it a generic pacakge is
not trivial, since autossh really wants config.h as generated by
./configure. Using the autotools infra in this case helps us easily
autoreconfiguring without to manual depend on all the autotools-relates
host packages.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>