[media] demux.h: fix a documentation warning

The kernel-doc parser didn't handle well the private:
tag. Rewrite it.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/dvb-core/demux.h

@@ -582,8 +582,10 @@ struct dmx_demux {
 
 	int (*get_pes_pids)(struct dmx_demux *demux, u16 *pids);
 
+	/* private: */
+
 	/*
-	 * private: Only used at av7110, to read some data from firmware.
+	 * Only used at av7110, to read some data from firmware.
 	 * As this was never documented, we have no clue about what's
 	 * there, and its usage on other drivers aren't encouraged.
 	 */