Input: atmel_mxt_ts - fix the firmware update

The automatic update mechanism will trigger an update if the
info block CRCs are different between maxtouch configuration
file (maxtouch.cfg) and chip.

The driver compared the CRCs without retrieving the chip CRC,
resulting always in a failure and firmware flashing action
triggered. Fix this issue by retrieving the chip info block
CRC before the check.

Note that this solution has the benefit that by reading the
information block and the object table into a contiguous region
of memory, we can verify the checksum at probe time. This means
we make sure that we are indeed talking to a chip that supports
object protocol correctly.

Using this patch on a kevin chromebook, the touchscreen and
touchpad drivers are able to match the CRC:

  atmel_mxt_ts 3-004b: Family: 164 Variant: 14 Firmware V2.3.AA Objects: 40
  atmel_mxt_ts 5-004a: Family: 164 Variant: 17 Firmware V2.0.AA Objects: 31
  atmel_mxt_ts 3-004b: Resetting device
  atmel_mxt_ts 5-004a: Resetting device
  atmel_mxt_ts 3-004b: Config CRC 0x573E89: OK
  atmel_mxt_ts 3-004b: Touchscreen size X4095Y2729
  input: Atmel maXTouch Touchscreen as /devices/platform/ff130000.i2c/i2c-3/3-004b/input/input5
  atmel_mxt_ts 5-004a: Config CRC 0x0AF6BA: OK
  atmel_mxt_ts 5-004a: Touchscreen size X1920Y1080
  input: Atmel maXTouch Touchpad as /devices/platform/ff140000.i2c/i2c-5/5-004a/input/input6

Signed-off-by: Nick Dyer <nick.dyer@shmanahar.org>
Acked-by: Benson Leung <bleung@chromium.org>
[Ezequiel: minor patch massage]
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>