[media] v4l: Remove documentation for nonexistend input field in v4l2_buffer

The input field in struct v4l2_buffer no longer exists but has been replaced
by a reserved field. Remove the field documentation.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

include/uapi/linux/videodev2.h

@@ -649,7 +649,6 @@ struct v4l2_plane {
  * @length:	size in bytes of the buffer (NOT its payload) for single-plane
  *		buffers (when type != *_MPLANE); number of elements in the
  *		planes array for multi-plane buffers
- * @input:	input number from which the video data has has been captured
  *
  * Contains data exchanged by application and driver using one of the Streaming
  * I/O methods.