iio:kfifo: Set update_needed to false after allocating a new buffer

update_needed is used to decide whether the kfifo buffer needs to be
re-allocated. It is set to true whenever the size of the buffer is changed. It
is never set to false though, causing the buffer to always be re-allocated.
Setting update_needed to false after the new buffer has been allocated fixes the
problem.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/kfifo_buf.c

@@ -38,6 +38,7 @@ static int iio_request_update_kfifo(struct iio_buffer *r)
 		kfifo_free(&buf->kf);
 		ret = __iio_allocate_kfifo(buf, buf->buffer.bytes_per_datum,
 				   buf->buffer.length);
+		buf->update_needed = false;
 	} else {
 		kfifo_reset_out(&buf->kf);
 	}