media: dvb_ca_en50221: New function dvb_ca_en50221_poll_cam_gone

The CAM poll code for the budget-av is exactly the same on several
places. Extracting the code to a new function improves maintainability.

Signed-off-by: Jasmin Jessich <jasmin@anw.at>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>