fixed a CEX in assert a_mepc_set_correct_after_irq

Created by: silabs-mateilga

This PR fixes a CEX in the mentioned assert, by recording the return address from a clic related pointer fetch and using it for comparison.

Note that the assert has not been proven to converge at the time of writing, but has been proven beyond the bound of the CEX this attempts to fix. PRing now, as the runtime for this is several days, maybe weeks.