Input: atmel_mxt_ts - don't report zero pressure from T9

If T9.CTRL DISAMP is set, then pressure is reported as zero. This means
some app layers (eg tslib) will ignore the contact.
Signed-off-by: NNick Dyer <nick.dyer@itdev.co.uk>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/atmel_mxt_ts.c

@@ -843,6 +843,10 @@ static void mxt_proc_t9_message(struct mxt_data *data, u8 *message)
 			mxt_input_sync(data);
 		}
 
+		/* if active, pressure must be non-zero */
+		if (!amplitude)
+			amplitude = MXT_PRESSURE_DEFAULT;
+
 		/* Touch active */
 		input_mt_report_slot_state(input_dev, MT_TOOL_FINGER, 1);
 		input_report_abs(input_dev, ABS_MT_POSITION_X, x);