[media] vb2: don't set index, don't start streaming for write()

Two fixes:

- there is no need to set the index when calling dqbuf: dqbuf will
overwrite it.
- __vb2_init_fileio already starts streaming for write(), so there is
no need to do it again in __vb2_perform_fileio. It can never have
worked anyway: either __vb2_init_fileio succeeds in starting streaming
or it is never going to happen.

Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/v4l2-core/videobuf2-core.c

···
 		memset(&fileio->b, 0, sizeof(fileio->b));
 		fileio->b.type = q->type;
 		fileio->b.memory = q->memory;
-		fileio->b.index = index;
 		ret = vb2_internal_dqbuf(q, &fileio->b, nonblock);
 		dprintk(5, "file io: vb2_dqbuf result: %d\n", ret);
 		if (ret)
···
 		 * Switch to the next buffer
 		 */
 		fileio->index = (index + 1) % q->num_buffers;
-
-		/*
-		 * Start streaming if required.
-		 */
-		if (!read && !q->streaming) {
-			ret = vb2_internal_streamon(q, q->type);
-			if (ret)
-				return ret;
-		}
 	}
 
 	/*