fixup simple type conversions where possible

src/video_core/pica_state.h

@@ -56,7 +56,7 @@ struct State {
         // Used to buffer partial vertices for immediate-mode rendering.
         Shader::InputVertex input_vertex;
         // Index of the next attribute to be loaded into `input_vertex`.
-        int current_attribute = 0;
+        u32 current_attribute = 0;
     } immediate;
 
     // This is constructed with a dummy triangle topology