clk: mediatek: update compatible string for MT7986 ethsys

Update compatible string of mt7986 ethsys clock driver to fit the
devicetree bindings document.

Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Link: https://lore.kernel.org/r/20220509090939.845-2-sam.shih@mediatek.com


Fixes: ec97d23c ("clk: mediatek: add mt7986 clock support")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>