Fix a bug in TPC_ModularEndcap_o1_v01.cpp when constructing Al frame position at the TPC endcap

The position of TPC Aluminum frame at the Endcap wasn't correct as expected because a /2 was missing in TPC_ModularEndcap_o1_v01.cpp file when placing the position of Al frame volume.

The figure below shows the structure of TPC Endcap before (left) and after (right) fix.