[media] rtl2830: prevent .read_status() when sleeping

Hardware is not accessible when device is sleeping.
Preventing such IOCTLs when sleep should be job of DVB CORE...

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>