[media] pvrusb2: fix sparse warning

drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2871:13: warning: symbol 'pvr2_hdw_get_detected_std' was not declared. Should it be static?

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>