platform/x86: surface3-wmi: Balance locking on error path

There is a possibility that lock will be left acquired.
Consolidate error path under out_free_unlock label.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>