Input: ads7846 - fix pressure reporting

On Zaurus, hx4700 and others pressure is reported inverted -- the lighter
the pressure, the bigger numerical value.

Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 09c8109..033233d 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -608,7 +608,7 @@
 
 		input_report_abs(input, ABS_X, x);
 		input_report_abs(input, ABS_Y, y);
-		input_report_abs(input, ABS_PRESSURE, Rt);
+		input_report_abs(input, ABS_PRESSURE, ts->pressure_max - Rt);
 
 		input_sync(input);
 #ifdef VERBOSE