docs: fix example of OoO write-back to scoreboard

Created by: cathales

Multiplication takes two cycles (1 cycle latency) and ALU takes one cycle (no latency). They share the same writeback port so it is not possible to issue an ALU instruction just after a MUL. So the example is wrong, but it is okay if we replace MUL by LOAD as it uses another write-back port.

Fix #1106 (closed)