iop-adma: use LIST_HEAD instead of LIST_HEAD_INIT

these three list_head are all local variables, but can also use LIST_HEAD.

Signed-off-by: Denis Cheng <crquan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>