Drop LIST_HEAD where the variable it declares is never used.

tmp_list has been declared since the introduction of the driver
and has never been used.  The two declarations of list were
introduced with the containing functions but were also not used.

The semantic patch that fixes this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
identifier x;
@@
- LIST_HEAD(x);
  ... when != x
// </smpl>

Fixes: dc78baa2 ("dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller")
Fixes: 4facfe7f ("dmaengine: hdmac: Split device_control")
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Vinod Koul <vkoul@kernel.org>