It is no need to check the packet[0] for sanity check when doing
elantech_packet_check_v4() function for fw_version = 0x470f01 touchpad.

Signed-off by: Duson Lin <dusonlin@emc.com.tw>
Reviewed-by: NUlrik De Bie <ulrik.debie-os@e2big.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>