Input: spaceball - fix parsing of movement data packets

The spaceball.c module was not properly parsing the movement reports
coming from the device.  The code read axis data as signed 16-bit
little-endian values starting at offset 2.

In fact, axis data in Spaceball movement reports are signed 16-bit
big-endian values starting at offset 3.  This was determined first by
visually inspecting the data packets, and later verified by consulting:
http://spacemice.org/pdf/SpaceBall_2003-3003_Protocol.pdf

If this ever worked properly, it was in the time before Git...

Signed-off-by: Leo L. Schwab <ewhac@ewhac.org>
Link: https://lore.kernel.org/r/20211221101630.1146385-1-ewhac@ewhac.org
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: ewhac

drivers/input/joystick/spaceball.c

@@ -19,6 +19,7 @@
 #include <linux/module.h>
 #include <linux/input.h>
 #include <linux/serio.h>
+#include <asm/unaligned.h>
 
 #define DRIVER_DESC	"SpaceTec SpaceBall 2003/3003/4000 FLX driver"
 
@@ -75,9 +76,15 @@ static void spaceball_process_packet(struct spaceball* spaceball)
 
 		case 'D':					/* Ball data */
 			if (spaceball->idx != 15) return;
-			for (i = 0; i < 6; i++)
+			/*
+			 * Skip first three bytes; read six axes worth of data.
+			 * Axis values are signed 16-bit big-endian.
+			 */
+			data += 3;
+			for (i = 0; i < ARRAY_SIZE(spaceball_axes); i++) {
 				input_report_abs(dev, spaceball_axes[i],
-					(__s16)((data[2 * i + 3] << 8) | data[2 * i + 2]));
+					(__s16)get_unaligned_be16(&data[i * 2]));
+			}
 			break;
 
 		case 'K':					/* Button data */