EDAC/igen6: Avoid segmentation fault on module unload

In the Linux kernel, the following vulnerability has been resolved:

EDAC/igen6: Avoid segmentation fault on module unload

The segmentation fault happens because:

During modprobe:

1. In igen6_probe(), igen6_pvt will be allocated with kzalloc()

2. In igen6_register_mci(), mci->pvt_info will point to

&igen6_pvt->imc[mc]

During rmmod:

1. In mci_release() in edac_mc.c, it will kfree(mci->pvt_info)

2. In igen6_remove(), it will kfree(igen6_pvt);

Fix this issue by setting mci->pvt_info to NULL to avoid the double

kfree.