juno/cdcel: Trust the HAL in mod_clock_drv_api

This driver implements an API defined by the HAL, so
we can be sure that the parameters passed to us do
not need to be sanitized.

Change-Id: I48efceeafaa423b2c3c573ca34c4ba86679e4084
Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>