platform/x86: dell-smbios-wmi: Add missing kfree in error-exit from run_smbios_call

As pointed out be Kees Cook if we return -EIO because the
obj->type != ACPI_TYPE_BUFFER, then we must kfree the
output buffer before the return.

Fixes: 1a258e67

 ("platform/x86: dell-smbios-wmi: Add new WMI dispatcher driver")
Reported-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210826140822.71198-1-hdegoede@redhat.com