staging: pi433: fix potential null dereference

Add a test for successful call to cdev_alloc() to avoid
potential null dereference. Issue reported by smatch.
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Fixes: 874bcba6 ("staging: pi433: New driver")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/pi433/pi433_if.c

@@ -1245,6 +1245,10 @@ static int pi433_probe(struct spi_device *spi)
 
 	/* create cdev */
 	device->cdev = cdev_alloc();
+	if (!device->cdev) {
+		dev_dbg(device->dev, "allocation of cdev failed");
+		goto cdev_failed;
+	}
 	device->cdev->owner = THIS_MODULE;
 	cdev_init(device->cdev, &pi433_fops);
 	retval = cdev_add(device->cdev, device->devt, 1);