ipmi: fix slave_addrs setting to actually work

Actually use the slave_addrs module parameter if it is specified, and make
things consistent about passing zero in for the slave address for the
default.

Signed-off-by: Bela Lubkin <blubkin@vmware.com>
Signed-off-by: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>