[media] DocBook: Fix documentation for struct v4l2_dv_timings

Fix this warning:
	include/media/v4l2-dv-timings.h:29: warning: cannot understand function prototype: 'const struct v4l2_dv_timings v4l2_dv_timings_presets[]; '

Unfortunately, currently, it seems that doc-nano doesn't support
documenting extern static vars.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

include/media/v4l2-dv-timings.h

@@ -23,7 +23,7 @@
 
 #include <linux/videodev2.h>
 
-/**
+/*
  * v4l2_dv_timings_presets: list of all dv_timings presets.
  */
 extern const struct v4l2_dv_timings v4l2_dv_timings_presets[];