console: SisUSB2VGA: Drop dummy con_font_get()

As done in commit:

  724ba8b3

 ("console/dummy: leave .con_font_get set to NULL")

This drops the dummy .con_font_get(), as it could leave arguments
uninitialized.

Cc: Thomas Winischhofer <thomas@winischhofer.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>