board: 7x30: Specify the correct min/max touch coordinates

The userspace interpolates touch coordinates based on max and
min values registered by the driver. These (max and min) values
are derived from the coordinates reported by the touch controller
(here TSC2007) for a given touchscreen.

Change-Id: I8a26c5d241131e32d3b73c4ecf2223e6ea835357
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>