Unify implementation of NWC Global Average Pooling across data types

PiperOrigin-RevId: 325386782
diff --git a/src/xnnpack/operator.h b/src/xnnpack/operator.h
index 6412693..5562fc9 100644
--- a/src/xnnpack/operator.h
+++ b/src/xnnpack/operator.h
@@ -242,8 +242,7 @@
 
   float input_scale;
   float output_scale;
-  uint8_t input_zero_point;
-  uint8_t kernel_zero_point;
+  int32_t input_zero_point;
   uint8_t output_zero_point;
   uint8_t output_min;
   uint8_t output_max;