IPMI: fix warning in ipmi_si_intf.c

trivial change: fix warning

Signed-off-by: Mijo Safradin <safradin@de.ibm.com>
Acked-by: Christian Krafft <krafft@de.ibm.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>