Input: zforce - don't invert the interrupt GPIO

Commit 2d538095

 ("Input: zforce_ts - convert to use the gpiod
interface") converted this driver to use the gpiod functions. These
functions take the active low property into account, so we don't have
to invert the result of gpiod_get_value_cansleep(). This has been
missed in that commit. Fix it.

Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>