CHROMIUM: Input: atmel_mxt_ts - make size/instances u16

CHROMIUM: Input: atmel_mxt_ts - make size/instances u16

Previously size and instances fields were u8 but could hold up to a value
of 255.  Since we now +1 to size and instances, they must be u16 to hold
the full size of up to 256.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium-os:27713
TEST=Confirm object table is read correctly:
     cat /sys/bus/i2c/devices/<dev>/object

Change-Id: Ib43baedf5c196b093713f2cec56f67e4ce93e60d
Reviewed-on: https://gerrit.chromium.org/gerrit/18548
Reviewed-by: Benson Leung <bleung@chromium.org>
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>