hw/net/stellaris_enet: Avoid unintended sign extension

Add a cast to avoid an unintended sign extension that
would mean we returned 0xffffffff in the high 32 bits
for an IA0 read if bit 31 in the MAC address was 1.
(This is harmless since we'll only be doing 4 byte
reads, but it could be confusing, so best avoided.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Message-id: 1392647854-8067-3-git-send-email-peter.maydell@linaro.org

hw/net/stellaris_enet.c

@@ -176,7 +176,8 @@ static uint64_t stellaris_enet_read(void *opaque, hwaddr offset,
         return val;
     case 0x14: /* IA0 */
         return s->conf.macaddr.a[0] | (s->conf.macaddr.a[1] << 8)
-               | (s->conf.macaddr.a[2] << 16) | (s->conf.macaddr.a[3] << 24);
+            | (s->conf.macaddr.a[2] << 16)
+            | ((uint32_t)s->conf.macaddr.a[3] << 24);
     case 0x18: /* IA1 */
         return s->conf.macaddr.a[4] | (s->conf.macaddr.a[5] << 8);
     case 0x1c: /* THR */