[media] media: dvb-core: prepare for enabling irq in complete()

Complete() will be run with interrupt enabled, so change to
spin_lock_irqsave().
These functions may be called inside URB->complete(), so use
spin_lock_irqsave().

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>