ipmi_si: fix crash on parisc

This patch fixes ipmi crash on parisc introduced in the kernel 4.15-rc.
The pointer io.io_setup is not initialized and thus it causes crash in
try_smi_init when attempting to call new_smi->io.io_setup.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>