Input: of_touchscreen - always issue warning if axis is not set up

Do issue warning about axis that is present in device tree but not specified
by the driver even in case of multi-touch axis as callers now tell us if they
expect multi-touch data or not.

Reviewed-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>