dmaengine: st_fdma: drop useless LIST_HEAD

Drop LIST_HEAD where the variable it declares is never used.

The declarations were introduced with the file, but the declared
variables were 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: 6b4cd727 ("dmaengine: st_fdma: Add STMicroelectronics FDMA engine driver support")
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Vinod Koul <vkoul@kernel.org>