ipynb: bug fix - copy.deepcopy throws an exception with memoized methods

Calling copy.deepcopy on the results dictionary of each experiment throws an
exception if among the results objects there are some with memoized methods.

Nevertheless, the deep copy was used to correctly copy the energy data
dictionary, therefore deep copy is now performed on that data only.

Signed-off-by: Michele Di Giorgio <michele.digiorgio@arm.com>