alsa-gobject: timer/seq: use const qualifier to self argument for getter API

[GitHub pull_request - opened <github@xxxxxxxxxxxxxxxx>]

alsa-project/alsa-gobject pull request #40 was opened from takaswie:

In ALSATimer and ALSASeq, some methods have prototype such that self argument don't have const qualifier even if it's getter method.

This patchset adds const qualifier to the methods.

Request URL   : https://github.com/alsa-project/alsa-gobject/pull/40
Patch URL     : https://github.com/alsa-project/alsa-gobject/pull/40.patch
Repository URL: https://github.com/alsa-project/alsa-gobject