V4L/DVB (7304): pvrusb2: add function pvr2_hdw_cmd_powerdown Call pvr2_hdw_cmd_powerdown to power down the device Signed-off-by: Michael Krufky <mkrufky@linuxtv.org> Signed-off-by: Mike Isely <isely@pobox.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>