sysfs: fix sysfs lockdep warning in ipmi code

This fixes a sysfs lockdep warning in the ipmi code.

Thanks to Eric Biederman and Yinghai Lu for the original versions of the
patch, unfortunatly they did not submit them in a form they could be
applied in.

Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>