arm64: dts: mediatek: mt6797: Fix 26M oscillator unit name

Update its unit name to oscillator-26m and remove the unneeded unit
address to fix a unit_address_vs_reg warning.

Fixes: 464c510f ("arm64: dts: mediatek: add mt6797 support")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221013152212.416661-9-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>