HID: hid-multitouch: ensure slots are initialized

In case a device does not provide the feature "Maximum Contact Count",
or set it at 0, the maxcontacts field may be at 0 while calling
input_mt_init_slots.

This patch ensures that hid-multitouch will allways report
ABS_MT_SLOT and ABS_MT_TRACKING_ID to the user space.

This corrects a bug found with some Ilitek devices that has been
integrated in 3.0-rc0.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@enac.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-multitouch.c

@@ -271,6 +271,8 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 			}
 			return 1;
 		case HID_DG_CONTACTID:
+			if (!td->maxcontacts)
+				td->maxcontacts = MT_DEFAULT_MAXCONTACT;
 			input_mt_init_slots(hi->input, td->maxcontacts);
 			td->last_slot_field = usage->hid;
 			td->last_field_index = field->index;
@@ -547,9 +549,6 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	if (ret)
 		goto fail;
 
-	if (!td->maxcontacts)
-		td->maxcontacts = MT_DEFAULT_MAXCONTACT;
-
 	td->slots = kzalloc(td->maxcontacts * sizeof(struct mt_slot),
 				GFP_KERNEL);
 	if (!td->slots) {