Fix build with clang 6.0.0

Clang 6.0.0 complains when initializing structure with { NULL }:

conf/domain_addr.c:1494:38: error: missing field 'type' initializer [-Werror,-Wmissing-field-initializers]
    virDomainDeviceInfo nfo = { NULL };

Use { 0 } instead to make it happy.
Signed-off-by: NRoman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

src/conf/domain_addr.c

@@ -1491,7 +1491,7 @@ virDomainVirtioSerialAddrAssign(virDomainDefPtr def,
                                 bool portOnly)
 {
     int ret = -1;
-    virDomainDeviceInfo nfo = { NULL };
+    virDomainDeviceInfo nfo = { 0 };
     virDomainDeviceInfoPtr ptr = allowZero ? &nfo : info;
 
     ptr->type = VIR_DOMAIN_DEVICE_ADDRESS_TYPE_VIRTIO_SERIAL;

tests/sysinfotest.c

@@ -91,7 +91,7 @@ sysinfotest_run(const char *test,
                 const char *cpuinfo,
                 const char *expected)
 {
-    struct testSysinfoData testdata = { NULL };
+    struct testSysinfoData testdata = { 0 };
     int ret = EXIT_FAILURE;
 
     testdata.func = func;