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_tabletDiagnosticMessage(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct aiptek *aiptek = dev_get_drvdata(dev);
	char *retMsg;

	switch (aiptek->diagnostic) {
	case AIPTEK_DIAGNOSTIC_NA:
		retMsg = "no errors\n";
		break;

	case AIPTEK_DIAGNOSTIC_SENDING_RELATIVE_IN_ABSOLUTE:
		retMsg = "Error: receiving relative reports\n";
		break;

	case AIPTEK_DIAGNOSTIC_SENDING_ABSOLUTE_IN_RELATIVE:
		retMsg = "Error: receiving absolute reports\n";
		break;

	case AIPTEK_DIAGNOSTIC_TOOL_DISALLOWED:
		if (aiptek->curSetting.pointerMode ==
		    AIPTEK_POINTER_ONLY_MOUSE_MODE) {
			retMsg = "Error: receiving stylus reports\n";
		} else {
			retMsg = "Error: receiving mouse reports\n";
		}
		break;

	default:
		return 0;
	}
	return snprintf(buf, PAGE_SIZE, retMsg);
}

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

	switch (aiptek->diagnostic) {
	case AIPTEK_DIAGNOSTIC_NA:
		retMsg = "no errors\n";
		break;

	case AIPTEK_DIAGNOSTIC_SENDING_RELATIVE_IN_ABSOLUTE:
		retMsg = "Error: receiving relative reports\n";
		break;

	case AIPTEK_DIAGNOSTIC_SENDING_ABSOLUTE_IN_RELATIVE:
		retMsg = "Error: receiving absolute reports\n";
		break;

	case AIPTEK_DIAGNOSTIC_TOOL_DISALLOWED:
		if (aiptek->curSetting.pointerMode ==
		    AIPTEK_POINTER_ONLY_MOUSE_MODE) {
			retMsg = "Error: receiving stylus reports\n";
		} else {
			retMsg = "Error: receiving mouse reports\n";
		}
		break;

	default:
		return 0;
	}
	return snprintf(buf, PAGE_SIZE, retMsg);
}
