ipmi: Fix NULL pointer dereference in ssif_probe

There is a potential execution path in which function ssif_info_find()
returns NULL, hence there is a NULL pointer dereference when accessing
pointer *addr_info*

Fix this by null checking *addr_info* before dereferencing it.

Addresses-Coverity-ID: 1473145 ("Explicit null dereferenced")
Fixes: e333054a91d1 ("ipmi: Fix I2C client removal in the SSIF driver")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>