ARM: dts: amlogic: meson8b: fix reference to unknown/untested PWM clock

ARM: dts: amlogic: meson8b: fix reference to unknown/untested PWM clock

Device-tree expects absent clocks to be specified as <0> (instead of
using <>). This fixes using the FCLK4/FCLK3 clocks as they are now
seen at their correct index (while before they were recognized, but at
the correct index - resulting in the hardware using a different clock
than what the kernel sees).

Fixes: dbf921861985 ("ARM: dts: amlogic: meson8b: switch to the new PWM controller binding")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250420164801.330505-3-martin.blumenstingl@googlemail.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>