[media] rtl28xxu: do not refcount rtl2832_sdr module

This driver, rtl28xxu, offers frontend service for rtl2832_sdr
module, thus we are producer and rtl2832_sdr module is consumer.
Due to that, reference counting should be done in way rtl2832_sdr
takes refrence to rtl28xxu. Remove wrong refcount.

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