V4L/DVB: gspca - sn9c20x: Correct onstack wait_queue_head declaration

Use DECLARE_WAIT_QUEUE_HEAD_ONSTACK to make lockdep happy

Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Jean-François Moine <moinejf@free.fr>
CC: Brian Johnson <brijohn@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>