fw_node: minor code refactoring to update information of unit
fw_node: minor code refactoring to update information of unit

The operation to update information requires system call. At present,
the operation has two callers. A caller requires error handling but
another doesn't. For the latter, instantiation of GError is not
necessarily required.

This commit applies minor code refactoring in a point of instantiation
of GError by caller side.

Signed-off-by: Takashi Sakamoto <d5ec7d0cd8074757a1f5eb708bc105c3065a65ea@sakamocchi.jp>

takaswie/libhinawa,takaswie/libhinawa