media: qcom: camss: remove a check for unavailable CAMSS endpoint

Media endpoints are not devices, and there is no valid or sane usecase,
when an endpoint on the ISP side is an unavailable device.

Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Tested-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>