tslib.c: get pressure resolution from device or tslib respectively
tslib.c: get pressure resolution from device or tslib respectively

For non-pressure devices, tslib creates pressure values between 0
and 255. For all others, tslib takes the device's values too, so we
should do so too.

Signed-off-by: Martin Kepplinger <5f224f582e4d41e2bdb8535d23e6b63d7ab1203d@ginzinger.com>

merge/xf86-input-tslib,merge/xf86-input-tslib