arm64: dts: mediatek: mt7986: fix reference to PWM in fan node

arm64: dts: mediatek: mt7986: fix reference to PWM in fan node

This fixes typo and resolves following validation error:
arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dtb: pwm-fan: pwms: [[54, 0, 10000], [0]] is too long
        from schema $id: http://devicetree.org/schemas/hwmon/pwm-fan.yaml#

Fixes: c26f779a2295 ("arm64: dts: mt7986: add pwm-fan and cooling-maps to BPI-R3 dts")
Cc: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20231116130816.4932-1-zajec5@gmail.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>