swiotlb: fix debugfs reporting of reserved memory pools

For io_tlb_nslabs, the debugfs code reports the correct value for a
specific reserved memory pool.  But for io_tlb_used, the value reported
is always for the default pool, not the specific reserved pool. Fix this.

Fixes: 5c850d3188 ("swiotlb: fix passing local variable to debugfs_create_ulong()")
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/swiotlb.c

@@ -930,7 +930,9 @@ EXPORT_SYMBOL_GPL(is_swiotlb_active);
 
 static int io_tlb_used_get(void *data, u64 *val)
 {
-	*val = mem_used(&io_tlb_default_mem);
+	struct io_tlb_mem *mem = data;
+
+	*val = mem_used(mem);
 	return 0;
 }
 DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_used, io_tlb_used_get, NULL, "%llu\n");
@@ -943,7 +945,7 @@ static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem,
 		return;
 
 	debugfs_create_ulong("io_tlb_nslabs", 0400, mem->debugfs, &mem->nslabs);
-	debugfs_create_file("io_tlb_used", 0400, mem->debugfs, NULL,
+	debugfs_create_file("io_tlb_used", 0400, mem->debugfs, mem,
 			&fops_io_tlb_used);
 }