mutex_destroy is not called in any error paths or in _remove. Just use
devm to do so.
Removed a pointless platform_set_devdata call. Not needed with all of
the devm conversions.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16630
Signed-off-by: Robert Marko <robimarko@gmail.com>