i3200_edac: Add a missing pci_disable_device() on the exit path

Currently, i3200_edac.c forgets to call pci_disable_device() during a
process of disabling device. This patch adds that call.

The problem was detected by Huqiu Liu.

Reported-by: Huqiu Liu <liuhq11@mails.tsinghua.edu.cn>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Link: http://lkml.kernel.org/r/1389587178-10167-1-git-send-email-mitake.hitoshi@gmail.com
Signed-off-by: Borislav Petkov <bp@suse.de>