of: unittest: simplify getting the adapter of a client

We have a dedicated pointer for that, so use it. Much easier to read and
less computation involved.
Reported-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/unittest.c

@@ -1946,7 +1946,7 @@ static int unittest_i2c_mux_probe(struct i2c_client *client,
 {
 	int i, nchans;
 	struct device *dev = &client->dev;
-	struct i2c_adapter *adap = to_i2c_adapter(dev->parent);
+	struct i2c_adapter *adap = client->adapter;
 	struct device_node *np = client->dev.of_node, *child;
 	struct i2c_mux_core *muxc;
 	u32 reg, max_reg;