arm64: dts: mt7896a: Fix unit_address_vs_reg warning for oscillator

Rename the oscillator fixed-clock to oscillator-40m and remove
the unit address to fix warnings.

arch/arm64/boot/dts/mediatek/mt7986a.dtsi:17.23-22.4: Warning
(unit_address_vs_reg): /oscillator@0: node has a unit name,
but no reg or ranges property

Fixes: 1f9986b2 ("arm64: dts: mediatek: add clock support for mt7986a")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221013152212.416661-2-angelogioacchino.delregno@collabora.com


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