media: qcom: camss: register camss media device before subdevices

A media device can and at least for sake of simplicity should be registered
before V4L2 devices including the ones added on async completion.

The change removes the second and out of camss_probe() media device
registration path, and it allows to get a working ISP media device
independently from connected or not sensor devices.

Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>