OMAPDSS: remove omap_dss_device->channel field

The 'channel' field in struct omap_dss_device is no longer used, and can
be removed.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Archit Taneja <archit@ti.com>

include/video/omapdss.h

@@ -765,9 +765,6 @@ struct omap_dss_device {
 	enum omap_display_type type;
 	enum omap_display_type output_type;
 
-	/* obsolete, to be removed */
-	enum omap_channel channel;
-
 	union {
 		struct {
 			u8 data_lines;