HACK: clk: rockchip: rk3399: Mark the PWM clock as critical

HACK: clk: rockchip: rk3399: Mark the PWM clock as critical

Until we get all the magic PWM regulator stuff solved with Boris's
wonderful upstream patches, let's just hack the PWM clock to be critical
so it never turns off.  Nuff said.

Change-Id: I99660b0b188413eb08030a3ae87c045c338b30db
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-on: https://chrome-internal-review.googlesource.com/254649
Reviewed-by: Stephen Barber <smbarber@google.com>
Tested-by: Doug Anderson <dianders@google.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
(Fixes the pclk_rkpwm_pmu into pmucru_critical_clock)