Tweak /proc/ipmi removal

Tweak /proc/ipmi removal

Driver does
	proc_mkdir("ipmi", NULL);
but
	remove_proc_entry(proc_ipmi_root->name, &proc_root);

This is OK and working if only slightly inconsistent.  Also changing
proc_root to NULL will help OpenVZ which has multiple proc roots and, as we
now know, requires matching parents in such cases.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>