udmabuf: Restore ubuf->unpin_list initialization

JIRA: https://issues.redhat.com/browse/RHEL-109567
Upstream Status: RHEL only
Fixes: 516519c ("Merge DRM changes from upstream v6.14..v6.15")

A change dropping the list initialization was included in the DRM
backport, however, the list is still in use.

Restore the list initialization code.

Signed-off-by: José Expósito <jexposit@redhat.com>

Author: jexposit

drivers/dma-buf/udmabuf.c

@@ -398,6 +398,7 @@ static long udmabuf_create(struct miscdevice *device,
 	if (!ubuf)
 		return -ENOMEM;
 
+	INIT_LIST_HEAD(&ubuf->unpin_list);
 	pglimit = ((u64)size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
 	for (i = 0; i < head->count; i++) {
 		if (!PAGE_ALIGNED(list[i].offset))