Input: adafruit-seesaw: fix "flat" value to avoid drifting

From: Michael Opdenacker <[email protected]>

Tests on 9 Adafruit Mini I2C Gamepad devices have shown that
the center X and Y values (when the joystick is left at its center position) deviate from 511, which is the center of the [0, 1023] value range:

Device     Center X   Vs. Expected (511) Center Y   Vs. Expected (511)
1          519        8                  493        -18
2          524        13                 518        7     Not very stable data!
3          508        -3                 531        20
4          531        20                 508        -3
5          505        -6                 521        10
6          519        8                  477        -34   Big outlier, ignored!
7          519        8                  524        13
8          524        13                 510        -1
9          517        6                  511        0

This change causes any X and Y value that is withing a [-20, +20] interval around 511, to be reported as centered. This avoids unwanted drifting (towards left, right, top or bottom) and makes playing with this device easier.

---
 drivers/input/joystick/adafruit-seesaw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 2b18451a0953..03eb181d5aef 100644
@@ -50,7 +50,7 @@
 
 #define SEESAW_JOYSTICK_MAX_AXIS	1023
 #define SEESAW_JOYSTICK_FUZZ		2
-#define SEESAW_JOYSTICK_FLAT		4
+#define SEESAW_JOYSTICK_FLAT		20
 
 #define SEESAW_GAMEPAD_POLL_INTERVAL_MS	16
 #define SEESAW_GAMEPAD_POLL_MIN		8