ACPI / IPMI: Cleanup several acpi_ipmi_device members

This (trivial) patch:
 1. Deletes a member of the acpi_ipmi_device, smi_data, which is not
    actually used.
 2. Updates a member of the acpi_ipmi_device, pnp_dev, which is only used
    by dev_warn() invocations, so changes it to a struct device.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reviewed-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>