hsi: nokia-modem: fix uninitialized device pointer

modem->device was never initialized. This resulted in logs such as:

[  241.386322] (NULL device *): CMT rst line change detected
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

drivers/hsi/clients/nokia-modem.c

@@ -162,6 +162,7 @@ static int nokia_modem_probe(struct device *dev)
 		return -ENOMEM;
 	}
 	dev_set_drvdata(dev, modem);
+	modem->device = dev;
 
 	irq = irq_of_parse_and_map(np, 0);
 	if (!irq) {