[PATCH] IPMI: Fix oops on ipmi_msghandler removal for non ipmi systems

When the ipmi_si module is loaded on a system without any ipmi device, it
fails with nodev.  It would be fine if all resources were freed.  A call to
device_unregister() is missing, resulting to a oops when you remove the
ipmi_msghandler.

Signed-off-by: Arnaud Patard <apatard@mandriva.com>
Acked-by: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>