[media] drivers/media/dvb-core/en50221: move code to dvb_ca_private_free()

Prepare for postponing the call until all file handles have been
closed.

[mchehab@osg.samsung.com: make checkpatch happy]
Signed-off-by: Max Kellermann <max@duempel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>