Input: elantech - fix V4 report decoding for module with middle key

Some touchpad has middle key and it will be indicated in bit 2 of packet[0].
We need to fix V4 formation's byte mask to prevent error decoding.
Signed-off-by: KT Liao <kt.liao@emc.com.tw>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/elantech.c

@@ -799,7 +799,7 @@ static int elantech_packet_check_v4(struct psmouse *psmouse)
 	else if (ic_version == 7 && etd->info.samples[1] == 0x2A)
 		sanity_check = ((packet[3] & 0x1c) == 0x10);
 	else
-		sanity_check = ((packet[0] & 0x0c) == 0x04 &&
+		sanity_check = ((packet[0] & 0x08) == 0x00 &&
 				(packet[3] & 0x1c) == 0x10);
 
 	if (!sanity_check)