staging: vboxvideo: remove unused variables

Fix compiler warnings:
vbox_mode.c:57:15: warning: variable ‘crtc_id’ set but not used
vbox_mode.c:581:25: warning: variable ‘vbox_connector’ set but not used

Signed-off-by: Paolo Cretaro <paolocretaro@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Michael Thayer <michael.thayer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>