btrfs: sink parameter len to alloc_extent_buffer

Because we're using globally known nodesize. Do the same for the sanity
test function variant.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 548cb54..9c20453 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1128,9 +1128,8 @@
 						 u64 bytenr)
 {
 	if (btrfs_test_is_dummy_root(root))
-		return alloc_test_extent_buffer(root->fs_info, bytenr,
-						root->nodesize);
-	return alloc_extent_buffer(root->fs_info, bytenr, root->nodesize);
+		return alloc_test_extent_buffer(root->fs_info, bytenr);
+	return alloc_extent_buffer(root->fs_info, bytenr);
 }