Input: st1232 - fix off-by-one error in resolution handling

Before, the maximum coordinates were fixed to (799, 479) or (319, 479),
depending on touchscreen controller type.  The driver was changed to
read the actual values from the touchscreen controller, but did not take
into account the returned values are not the maximum coordinates, but
the touchscreen resolution (e.g. 800 and 480).

Fix this by subtracting 1.

Fixes: 3a54a215 ("Input: st1232 - add support resolution reading")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201229162601.2154566-2-geert+renesas@glider.beSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/st1232.c

@@ -85,8 +85,8 @@ static int st1232_ts_read_resolution(struct st1232_ts_data *ts, u16 *max_x,
 
 	buf = ts->read_buf;
 
-	*max_x = ((buf[0] & 0x0070) << 4) | buf[1];
-	*max_y = ((buf[0] & 0x0007) << 8) | buf[2];
+	*max_x = (((buf[0] & 0x0070) << 4) | buf[1]) - 1;
+	*max_y = (((buf[0] & 0x0007) << 8) | buf[2]) - 1;
 
 	return 0;
 }