firmware_loader: Fix use-after-free during unregister

In the Linux kernel, the following vulnerability has been resolved:

firmware_loader: Fix use-after-free during unregister

In the following code within firmware_upload_unregister(), the call to

device_unregister() could result in the dev_release function freeing the

fw_upload_priv structure before it is dereferenced for the call to

module_put(). This bug was found by the kernel test robot using

CONFIG_KASAN while running the firmware selftests.

device_unregister(&fw_sysfs->dev);

module_put(fw_upload_priv->module);

The problem is fixed by copying fw_upload_priv->module to a local variable

for use when calling device_unregister().