EDAC: Use edac_debugfs_remove_recursive()

EDAC: Use edac_debugfs_remove_recursive()

debugfs_remove() is used to remove a file or a directory from the
debugfs filesystem, but mci->debugfs might not empty.

This can be triggered by the following sequence:

1) Enable CONFIG_EDAC_DEBUG
2) insmod an EDAC module (like i3000_edac or similar)
3) rmmod this module
4) we can see files remaining under <debugfs_mountpoint>/edac/ like
   "fake_inject", for example.

Removing edac_core then, causes a NULL pointer dereference.

Reported-by: Yun Wu (Abel) <wuyun.wu@huawei.com>
Signed-off-by: Tan Xiaojun <tanxiaojun@huawei.com>
Cc: Doug Thompson <dougthompson@xmission.com>
Cc: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1444787364-104353-1-git-send-email-tanxiaojun@huawei.com
Signed-off-by: Borislav Petkov <bp@suse.de>