Squeezebox: Only flag media position as updated when it really has changed

[molobrakos]

Description:

To prevent logs, database, etc to be spammed with state updates, the media_position_updated_at property should only change when the media position has in fact changed.

This is analogous to e.g. https://github.com/home-assistant/home-assistant/blob/dev/homeassistant/components/media_player/vlc.py#L72

Related issue (if applicable): fixes #

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.github.io#<home-assistant.github.io PR number goes here>

Example entry for configuration.yaml (if applicable):

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[houndci-bot]

line too long (89 > 79 characters)

[syssi]

LGTM.