Input: of_touchscreen - explicitly choose axis

The 'axis + 1' calculation is implicit and potentially error prone.
Moreover, few lines before the axis is set explicitly for both X and Y.

Do the same when retrieving different properties for X and Y.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200303180917.12563-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>