media: ccs: Don't complain about missing "clock-frequency" property

The clock frequency is often available via the clock itself and not read
by the driver from the "clock-frequency" property. Don't complain if the
property doesn't exist.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>