swiotlb: Don't DoS us with 'swiotlb buffer is full' (v2)

There is no need for that so lets use ratelimiting.
Also add some extra information to be helpful.
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
[v2: s/ld/zs on the printk]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

lib/swiotlb.c

@@ -505,7 +505,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 
 not_found:
 	spin_unlock_irqrestore(&io_tlb_lock, flags);
-	dev_warn(hwdev, "swiotlb buffer is full\n");
+	if (printk_ratelimit())
+		dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", size);
 	return SWIOTLB_MAP_ERROR;
 found:
 	spin_unlock_irqrestore(&io_tlb_lock, flags);