Input: aiptek - fix crash on detecting device without endpoints

The aiptek driver crashes in aiptek_probe() when a specially crafted USB
device without endpoints is detected. This fix adds a check that the device
has proper configuration expected by the driver. Also an error return value
is changed to more matching one in one of the error paths.

Reported-by: Ralf Spenneberg <ralf@spenneberg.net>
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
store_tabletWheel(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
	struct aiptek *aiptek = dev_get_drvdata(dev);
	int err, w;

	err = kstrtoint(buf, 10, &w);
	if (err)
		return err;

	aiptek->newSetting.wheel = w;
	return count;
}

store_tabletWheel(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
	struct aiptek *aiptek = dev_get_drvdata(dev);
	int err, w;

	err = kstrtoint(buf, 10, &w);
	if (err)
		return err;

	aiptek->newSetting.wheel = w;
	return count;
}
