pwm: tiehrpwm: Update shadow register for disabling PWMs

commit b00ef530 upstream.

It must be made sure that immediate mode is not already set, when
modifying shadow register value in ehrpwm_pwm_disable(). Otherwise
modifications to the action-qualifier continuous S/W force
register(AQSFRC) will be done in the active register.
This may happen when both channels are being disabled. In this case,
only the first channel state will be recorded as disabled in the shadow
register. Later, when enabling the first channel again, the second
channel would be enabled as well. Setting RLDCSF to zero, first, ensures
that the shadow register is updated as desired.

Fixes: 38dabd91 ("pwm: tiehrpwm: Fix disabling of output of PWMs")
Signed-off-by: Christoph Vogtländer <c.vogtlaender@sigma-surface-science.com>
[vigneshr@ti.com: Improve commit message]
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>