arm64: dts: qcom: sc7280: Adjust zombie PWM frequency

Tune the PWM to solve screen flashing issue and high frequency noise.
While at it, the comment for the PWM settings incorrectly said we were
using a 5kHz duty cycle. It should have said "period", not "duty cycle".
Correct this while updating the values.

Signed-off-by: Owen Yang <ecs.taipeikernel@gmail.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230213105803.v2.1.I610cef0ead2d5df1f7bd18bc0e0ae040b03725d0@changeid