platform/x86: huawei-wmi: Don't leak memory on the exit

We have to clean memory resources allocated during init.

Fixes: 7532afb35012 ("platform/x86: huawei-wmi: Move to platform driver")
Cc: Ayman Bagabas <ayman.bagabas@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>