Ref-model generate build warning fix

Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>
Change-Id: I1fb734285c60f71a74a5815e76ace51ace719400
diff --git a/reference_model/src/generate/generate_fixed_data.cc b/reference_model/src/generate/generate_fixed_data.cc
index d83ee58..3d4ee3e 100644
--- a/reference_model/src/generate/generate_fixed_data.cc
+++ b/reference_model/src/generate/generate_fixed_data.cc
@@ -37,7 +37,7 @@
             int32_t* outData            = reinterpret_cast<int32_t*>(data);
             std::vector<int32_t> inData = cfg.fixedDataInfo.data;
             const auto T                = TosaReference::numElementsFromShape(cfg.shape);
-            if (T != inData.size())
+            if (T != static_cast<int64_t>(inData.size()))
             {
                 WARNING("[Generator][FD] Size does not match.");
                 return false;