dmaengine: dw-edma: Remove an unused variable

'head' is unused, remove it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/46e071be21fbc5ac5c35d4796a7e4249e94c3a77.1633847306.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Vinod Koul <vkoul@kernel.org>