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>
static ssize_t show_tabletMouseMiddle(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct aiptek *aiptek = dev_get_drvdata(dev);

	return snprintf(buf, PAGE_SIZE, "%s\n",
			map_val_to_str(mouse_button_map,
					aiptek->curSetting.mouseButtonMiddle));
}

static ssize_t show_tabletMouseMiddle(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct aiptek *aiptek = dev_get_drvdata(dev);

	return snprintf(buf, PAGE_SIZE, "%s\n",
			map_val_to_str(mouse_button_map,
					aiptek->curSetting.mouseButtonMiddle));
}
