pwm: lpss: Log error from pwm_lpss_is_updating() if the update bit is still set

pwm_lpss_is_updating() does a sanity check which should never fail.
If the check does actually fail that is worth logging an error,
especially since this means that we will skip making the requested
changes to the PWM settings.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>