coresight: Refactor runtime PM

The validation for driver data pointers and clock pointers are redundant
in the runtime PM callbacks.  After a driver's probing, its driver data
and clocks have been initialized successfully, this ensures it is safe
to access driver data and clocks in the runtime PM callbacks.  A corner
case is a clock pointer is NULL, in this case, the clock core layer can
handle it properly.  So remove these redundant checking.

In runtime resume, respect values returned from clock function and add
error handling.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250731-arm_cs_fix_clock_v4-v6-10-1dfe10bb3f6f@arm.com