[media] rtl2832_sdr: fixing v4l2-compliance issues

Fix rtl2832_sdr driver v4l2-compliance issues.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>