HID: wacom: fix Bamboo ONE oops

Looks like recent changes in the Wacom driver made the Bamboo ONE crashes.
The tablet behaves as if it was a regular Bamboo device with pen, touch
and pad, but there is no physical pad connected to it.
The weird part is that the pad is still sending events and given that
there is no input node connected to it, we get  anull pointer exception.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1317116

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.c

@@ -2425,6 +2425,17 @@ void wacom_setup_device_quirks(struct wacom *wacom)
 		}
 	}
 
+	/*
+	 * Hack for the Bamboo One:
+	 * the device presents a PAD/Touch interface as most Bamboos and even
+	 * sends ghosts PAD data on it. However, later, we must disable this
+	 * ghost interface, and we can not detect it unless we set it here
+	 * to WACOM_DEVICETYPE_PAD or WACOM_DEVICETYPE_TOUCH.
+	 */
+	if (features->type == BAMBOO_PEN &&
+	    features->pktlen == WACOM_PKGLEN_BBTOUCH3)
+		features->device_type |= WACOM_DEVICETYPE_PAD;
+
 	/*
 	 * Raw Wacom-mode pen and touch events both come from interface
 	 * 0, whose HID descriptor has an application usage of 0xFF0D