When applying touchscreen parameters specified in device tree let's make
sure we keep whatever setup was done by the driver and not reset the
missing values to zero.
Reported-by: NPavel Machek <pavel@ucw.cz>
Tested-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>