dmaengine: ppc4xx: Make use of the helper macro LIST_HEAD()

Replace "struct list_head head = LIST_HEAD_INIT(head)" with
"LIST_HEAD(head)" to simplify the code.

Signed-off-by: Cai Huoqing <cai.huoqing@linux.dev>
Link: https://lore.kernel.org/r/20220209032221.37211-1-cai.huoqing@linux.dev


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