fb: fix atyfb build warning

Fix build warning when neither of CONFIG_FB_ATY_GX or
CONFIG_FB_ATY_CT is enabled, since ARRAY_SIZE(aty_chips) is 0 in
that case.

drivers/video/aty/atyfb_base.c:437:11: warning: overflow in implicit constant conversion [-Woverflow]
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Cc:	Paul Mackerras <paulus@samba.org>
Cc:	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:	linux-fbdev@vger.kernel.org
Cc:	Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc:	Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/aty/atyfb_base.c

@@ -434,8 +434,8 @@ static int correct_chipset(struct atyfb_par *par)
 	const char *name;
 	int i;
 
-	for (i = ARRAY_SIZE(aty_chips) - 1; i >= 0; i--)
-		if (par->pci_id == aty_chips[i].pci_id)
+	for (i = ARRAY_SIZE(aty_chips); i > 0; i--)
+		if (par->pci_id == aty_chips[i - 1].pci_id)
 			break;
 
 	if (i < 0)