w32: Fix assuan_connect_fd

* src/assuan-socket-connect.c (assuan_socket_connect_fd): Map fd to
assuan_fd_t.

This function is actually not used by GnuPG. The function should have
taken an assuan_fd but given that it did not we use our usual mapping
from Windows libc fds to an assuan fd.

• Signed-off-by: Werner Koch <wk@gnupg.org>