V4L/DVB (9144): af9015: enable Maxlinear mxl5005s tuner RSSI

- enable Maxlinear mxl5005s tuner RSSI

Thaks to Jose Alberto for finding this setting.

Thanks-to: Jose Alberto Reguero <jareguero@telefonica.net>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>