Mark static arrays as thread-safe in EcalScDetId

The static analyzer was given a false positive for the static arrays in EcalScDetId.
Used the thread safe macro to tell the static analyzer to ignore them. This is appropriate
since the static arrays are filled once in a thread safe way (std::call_once) and then
only read and never modified.
Future versions of C++ will give away to fill the arrays at construction time and therefore
we will be able to change them to const.