Input: ti_am335x_tsc - warn about incorrect spelling

In the hopes that people run new kernels on their devices, let's add a
warning message asking users to have their DTS file fixed.

The goal is that by Linux 4.0 we will be able to remove support for the
bogus version of our touchscreen's DTS.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>