server: silence build warning
server: silence build warning

The commit fixes this build warning:

====
src/server.c:223:8: warning: ‘privkey’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     rc = ssh_pki_export_privkey_to_pubkey(*privkey, &pubkey);
        ^
src/server.c:243:11: note: ‘privkey’ was declared here
   ssh_key privkey;
====

Signed-off-by: Luka Perkov <fe6d8aafe911b69ec3eecb89e7941038c0d25a22@sartura.hr>
Reviewed-by: Andreas Schneider <5be00ddc76278cf6077f5047ca3384a88460c671@cryptomilk.org>

mwgoldsmith/ssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/libssh