clk: meson: use devm_of_clk_add_hw_provider

There is no remove callbacks in meson's clock controllers and
of_clk_del_provider is never called if of_clk_add_hw_provider has been
executed, introducing a potential memory leak.
Fixing this by the using the devm variant.

In reality, the leak would never happen since these controllers are
never unloaded once in use ... still, this is worth cleaning.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>