Milton Miller noticed a free-after-use problem in the cleanup path of a
failed module load.

The problem is that mod is moved to point from the sucked-in file
(always freed last) to the module core, after which time the
"free(mod->core), reference mod->percpu" sequence is bogus, eg.  when
the module_init function fails.

This is fixed by keeping the pointer in a local variable, which solves
the problem. We no longer need to reference the free'd data structure.