[media] au0828: Fix DVB resume when streaming

When DVB is streaming and suspend is called, it will call
au0828_stop_transport(), with will clean the streaming flag.

Due to that, stop_urb_transfer() will be called twice,
causing an oops.

So, we need another flag to be used at resume, telling it
to restart DVB.

While here, add a logic at stop_urb_transfer() to prevent
it of being called twice, and convert the usb_streaming
flag into boolean.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>