timer: query: use GFileError to report error

timer: query: use GFileError to report error

In design of ALSA timer, timer character device is not corresponding to
each substance of timer device. It's a kind of interface to query and
operate. Applications adds user instance and operates it to use its
services. Nevertheless, the interface has some functionality without
adding the user instances.

For the functionality, this library has global functions. The functions
are not relevant to the user instance, therefore it's not reasonable to
use error domain specific to the user instance.

This commit uses GFileError to report errors in the global functions.

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