ipmi: Cleanup oops on initialization failure

Commit 93c303d2 "ipmi_si: Clean up shutdown a bit" didn't
copy the behavior of the cleanup in one spot, it needed to
check for a non-NULL interface before cleaning it up.
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Tested-by: Meelis Roos <mroos@linux.ee>

drivers/char/ipmi/ipmi_si_intf.c

@@ -2088,8 +2088,10 @@ static int try_smi_init(struct smi_info *new_smi)
 	return 0;
 
 out_err:
-	ipmi_unregister_smi(new_smi->intf);
-	new_smi->intf = NULL;
+	if (new_smi->intf) {
+		ipmi_unregister_smi(new_smi->intf);
+		new_smi->intf = NULL;
+	}
 
 	kfree(init_name);