Input: vsxxxaa - fix code dropping bytes from queue

I believe the intent of the code was to drop oldest bytes from the queue,
not the latest if we drop one byte and both latest and some oldest of we
are dropping more than one.
Acked-by: NJan-Benedict Glaw <jbglaw@lug-owl.de>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/vsxxxaa.c

@@ -128,7 +128,7 @@ static void vsxxxaa_drop_bytes(struct vsxxxaa *mouse, int num)
 	if (num >= mouse->count) {
 		mouse->count = 0;
 	} else {
-		memmove(mouse->buf, mouse->buf + num - 1, BUFLEN - num);
+		memmove(mouse->buf, mouse->buf + num, BUFLEN - num);
 		mouse->count -= num;
 	}
 }