vdpa/mlx5: Fix suboptimal range on iotlb iteration

The starting iova address to iterate iotlb map entry within a range
was set to an irrelevant value when passing to the itree_next()
iterator, although luckily it doesn't affect the outcome of finding
out the granule of the smallest iotlb map size. Fix the code to make
it consistent with the following for-loop.

Fixes: 94abbccdf291 ("vdpa/mlx5: Add shared memory registration code")
Signed-off-by: Si-Wei Liu <[e-mail]>
Signed-off-by: Dragos Tatulea <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Acked-by: Jason Wang <[e-mail]>

drivers/vdpa/mlx5/core/mr.c

···
 	unsigned long lgcd = 0;
 	int log_entity_size;
 	unsigned long size;
-	u64 start = 0;
 	int err;
 	struct page *pg;
 	unsigned int nsg;
···
 	struct device *dma = mvdev->vdev.dma_dev;
 
 	for (map = vhost_iotlb_itree_first(iotlb, mr->start, mr->end - 1);
-	     map; map = vhost_iotlb_itree_next(map, start, mr->end - 1)) {
+	     map; map = vhost_iotlb_itree_next(map, mr->start, mr->end - 1)) {
 		size = maplen(map, mr);
 		lgcd = gcd(lgcd, size);
-		start += size;
 	}
 	log_entity_size = ilog2(lgcd);