x86, microcode, AMD: Fix use after free in free_cache()

list_for_each_entry_reverse() dereferences the iterator, but we already
freed it. I don't see a reason that this has to be done in reverse order
so change it to use list_for_each_entry_safe().

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>