drm/sun4i: Don't skip TCONs if they don't have channel 0

TV TCONs (channel 1 only) are always connected to TV or HDMI encoder.
Because of that, all output endpoints on such TCON node will point to a
encoder which is part of component framework.

Correct current graph traversing algorithm in such way that it doesn't
skip output enpoints with id 0 on TV TCONs.

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/20180625120304.7543-10-jernej.skrabec@siol.net