ipmi: Replace guid_copy() with import_guid() where it makes sense

There is a specific API to treat raw data as GUID, i.e. import_guid().
Use it instead of guid_copy() with explicit casting.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Message-Id: <20200422130348.38749-1-andriy.shevchenko@linux.intel.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>