Drop LIST_HEAD where the variable it declares is never used.

The variable has not been used since the function was introduced
in 740aa957 ("dmaengine: pl330: Split device_control").

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

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

Fixes: 740aa957 ("dmaengine: pl330: Split device_control")
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Vinod Koul <vkoul@kernel.org>