staging: media: tegra-video: vi: improve logic of source requesting

staging: media: tegra-video: vi: improve logic of source requesting

By default tegra_channel_get_remote_csi_subdev returns next device in pipe
assuming it is CSI but in case of Tegra20 and Tegra30 it can also be VIP
or even HOST.

Define tegra_channel_get_remote_csi_subdev within CSI and add check if
returned device is actually CSI by comparing subdevice operations.

Previous tegra_channel_get_remote_csi_subdev definition in VI rename to
tegra_channel_get_remote_bridge_subdev and use it only in VI driver since
core VI driver does not care about source and does not call any specific
functions.

Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com> # tegra20, parallel camera
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>