media: ccs: Add a sanity check for external clock frequency

The driver depends on the external clock frequency. Add a sanity check for
the frequency, by returning an error from probe if it's zero.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>