[media] media/au0828: Fix IR stop, poll to not access device during disconnect

au0828 IR stop and poll routines continue to access device
while usb disconnect is in progress. There is small window
between device disconnect and usb interface is set to null.
This results in filling the log with several of the following
error messages. Fix it to detect device disconnect condition
and avoid device access.

Nov 20 18:58:02 anduin kernel: [  102.949819] au0828: au0828_usb_disconnect()
Nov 20 18:58:02 anduin kernel: [  102.950046] au0828: send_control_msg() Failed sending control message, error -71.
Nov 20 18:58:02 anduin kernel: [  102.950052] au0828: send_control_msg() Failed sending control message, error -19.
Nov 20 18:58:02 anduin kernel: [  102.950056] au0828: send_control_msg() Failed sending control message, error -19.
Nov 20 18:58:02 anduin kernel: [  102.950061] au0828: send_control_msg() Failed sending control message, error -19.
Nov 20 18:58:02 anduin kernel: [  102.950065] au0828: recv_control_msg() Failed receiving control message, error -19.
Nov 20 18:58:02 anduin kernel: [  102.950069] au0828: recv_control_msg() Failed receiving control message, error -19.
Nov 20 18:58:02 anduin kernel: [  102.950072] au0828: recv_control_msg() Failed receiving control message, error -19.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>