s390: fix build on 32 bit host

Building on 32 bit host we get:
hw/s390-virtio.c: In function ‘s390_init’:
hw/s390-virtio.c:184: error: integer constant is too large for ‘unsigned long’ type
64 bit values must be ULL.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Acked-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

hw/s390-virtio.c

@@ -181,7 +181,7 @@ static void s390_init(ram_addr_t ram_size,
 
         cpu_synchronize_state(env);
         env->psw.addr = KERN_IMAGE_START;
-        env->psw.mask = 0x0000000180000000UL;
+        env->psw.mask = 0x0000000180000000ULL;
     }
 
     if (initrd_filename) {