Revert order in VGA device choice

Before change "Simplify VGA card discovery"
(http://review.coreboot.org/#/c/1255/)
coreboot was setting up VGA for the last found VGA device.
After this change it setting up VGA for the first found.
This change broke compatibility to my Supermicro H8QGI board.
Revert order back to old to save compatibility for this board
(and maybe any other boards)

Change-Id: Id5f2be60f95298059651c26133806e2694ff60aa
Signed-off-by: Kostr <aladyshev@nicevt.ru>
Reviewed-on: http://review.coreboot.org/1561
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/devices/device.c

@@ -732,7 +732,7 @@ static void set_vga_bridge_bits(void)
 
 		if (dev->on_mainboard) {
 			vga_onboard = dev;
-		} else if (!vga) {
+		} else {
 			vga = dev;
 		}