HID: wacom: Expect 'touch_max' touches if HID_DG_CONTACTCOUNT not present

When introduced in commit 1b5d514, the check 'if (hid_data->cc_index >= 0)'
in 'wacom_wac_finger_pre_report' was intended to switch where the driver
got the expected number of contacts from: HID_DG_CONTACTCOUNT if the usage
was present, or 'touch_max' otherwise. Unfortunately, an oversight worthy
of a brown paper bag (specifically, that 'cc_index' could never be negative)
meant that the latter 'else' clause would never be entered.

The patch prior to this one introduced a way for 'cc_index' to be negative,
but only if HID_DG_CONTACTCOUNT is present in some report _other_ than the
one being processed. To ensure the 'else' clause is also entered for devices
which don't have HID_DG_CONTACTCOUNT on _any_ report, we add the additional
constraint that 'cc_report' be non-zero (which is true only if the usage is
present in some report).

Cc: stable@vger.kernel.org
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.c

@@ -1740,8 +1740,8 @@ static void wacom_wac_finger_pre_report(struct hid_device *hdev,
 			}
 		}
 	}
-
-	if (hid_data->cc_index >= 0) {
+	if (hid_data->cc_report != 0 &&
+	    hid_data->cc_index >= 0) {
 		struct hid_field *field = report->field[hid_data->cc_index];
 		int value = field->value[hid_data->cc_value_index];
 		if (value)