qemu: qapi: Fix return value of impossible case in virQEMUQAPISchemaTraverse

The return statement after the infinite loop without a break is there to
appease the compiler. Make it return NULL as it would be a failure if
control flow reaches that point.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_qapi.c

@@ -164,7 +164,7 @@ virQEMUQAPISchemaTraverse(const char *baseName,
         query++;
     }
 
-    return base;
+    return NULL;
 }