Input: pxa930_trkball - fix write timeout handling

With a postfix decrement i reaches -1 rather than 0,
but after the loop it is tested whether it has become 0.
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/mouse/pxa930_trkball.c

@@ -83,7 +83,7 @@ static int write_tbcr(struct pxa930_trkball *trkball, int v)
 
 	__raw_writel(v, trkball->mmio_base + TBCR);
 
-	while (i--) {
+	while (--i) {
 		if (__raw_readl(trkball->mmio_base + TBCR) == v)
 			break;
 		msleep(1);