V4L/DVB (3827): Cx88-blackbird: clean up the buffers when closing the MPEG stream

This patch cleans up the buffer queue when the MPEG stream is closed,
preventing the message, 'cx8802_timeout'

Signed-off-by: Valentin Zagura <puthre@gmail.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>