firmware_loader: introduce __free() cleanup hanler

Define cleanup handler using facilities from linux/cleanup.h to simplify
error handling in code using firmware loader. This will allow writing code
like this:

int driver_update_firmware(...)
{
	const struct firmware *fw_entry __free(firmware) = NULL;
	int error;

	...
	error = request_firmware(&fw_entry, fw_name, dev);
	if (error) {
		dev_err(dev, "failed to request firmware %s: %d",
			fw_name, error);
		return error;
	}

	error = check_firmware_valid(fw_entry);
	if (error)
		return error;

	guard(mutex)(&instance->lock);

	error = use_firmware(instance, fw);
	if (error)
		return error;

	return 0;
}

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Luis Chamberalin <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/ZaeQw7VXhnirX4pQ@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>