Fix mistakes in checking return values

Thre was a syntax error in checking virRegisterStateDriver in
the remote driver, and bogus checking of a void return type
of virDomainConfNWFilterRegister in nwfilter.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/nwfilter/nwfilter_driver.c

@@ -720,7 +720,6 @@ int nwfilterRegister(void) {
         return -1;
     if (virRegisterStateDriver(&stateDriver) < 0)
         return -1;
-    if (virDomainConfNWFilterRegister(&domainNWFilterDriver) < 0)
-        return -1;
+    virDomainConfNWFilterRegister(&domainNWFilterDriver);
     return 0;
 }

src/remote/remote_driver.c

@@ -7840,7 +7840,7 @@ remoteRegister(void)
     if (virRegisterNWFilterDriver(&nwfilter_driver) < 0)
         return -1;
 #ifdef WITH_LIBVIRTD
-    if (virRegisterStateDriver(&state_driver) == -1) < 0)
+    if (virRegisterStateDriver(&state_driver) < 0)
         return -1;
 #endif