[media] em28xx-dvb: stop URBs when stopping the streaming

Stop the URBs in em28xx_stop_streaming(), so that em28xx_irq_callback()
cannot be called after the streaming has stopped.

This should eliminate the crashes reported by Antti Palosaari and the warnings
reported by Andy Furniss.

Signed-off-by: Gianluca Gennari <gennarone@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

diff --cc drivers/media/video/em28xx/em28xx-core.c
Simple merge

diff --cc drivers/media/video/em28xx/em28xx-dvb.c
Simple merge

diff --cc drivers/media/video/em28xx/em28xx.h
Simple merge