clk: mediatek: Add MODULE_LICENSE() where missing

In order to successfully build clock drivers as modules it is required
to declare a module license: add it where missing.
While at it, also change the MODULE_LICENSE text from "GPL v2" to
"GPL" (which means the same) on clk-mt7981-eth.c.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Miles Chen <miles.chen@mediatek.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org> # MT8183, MT8192, MT8195 Chromebooks
Link: https://lore.kernel.org/r/20230306140543.1813621-38-angelogioacchino.delregno@collabora.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>