openssh: use wget instead of uscan to download the orig tarball

In Precise, uscan seems to fail:

uscan --download-current-version --rename
uscan warning: unrecognised option pgpsigurlmangle=s/$/.asc/
uscan warning: In debian/watch no matching files for watch line
  ftp://ftp.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-(.*)\.tar\.gz
make: *** [get-orig-source] Error 1