[Fix] getCPUPtr() function for MatMul forward use

include/aidge/backend/cpu/data/GetCPUPtr.h

@@ -12,13 +12,16 @@
 #ifndef AIDGE_CPU_DATA_GETCPUPTR_H_
 #define AIDGE_CPU_DATA_GETCPUPTR_H_
 
+#include <cstddef>
+#include <memory>
+
 #include "aidge/data/Tensor.hpp"
 
 namespace Aidge {
-inline void *getCPUPtr(std::shared_ptr<Aidge::Data> const &data) {
+inline void *getCPUPtr(std::shared_ptr<Aidge::Data> const &data, const std::size_t offset = 0) {
   const auto tensor = std::static_pointer_cast<Tensor>(data);
-  return tensor->getImpl()->hostPtr(tensor->getImplOffset());
+  return tensor->getImpl()->hostPtr(tensor->getImplOffset() + offset);
 }
 } // namespace Aidge
 
-#endif // AIDGE_CPU_DATA_GETCPUPTR_H_
\ No newline at end of file
+#endif // AIDGE_CPU_DATA_GETCPUPTR_H_