ipmi_si: fix memory leak on new_smi

The error exit path omits kfree'ing the allocated new_smi, causing a memory
leak.  Fix this by kfree'ing new_smi.

Detected by CoverityScan, CID#14582571 ("Resource Leak")

Fixes: 7e030d6d ("ipmi: Prefer ACPI system interfaces over SMBIOS ones")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>