TV TCONs are always connected to TV or HDMI encoder, so it doesn't make
sense to check if panel or bridge is connected to them.

Check if TCON has channel 0 and only then check for connected panel or
bridges.
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625120304.7543-13-jernej.skrabec@siol.net