coresight: sysfs: Use source's path pointer for path control

coresight: sysfs: Use source's path pointer for path control

Since the path pointer is stored in the source's structure, retrieve it
directly when disabling the path.

As a result, the global variables used for caching path pointers are no
longer needed. Remove them to simplify the code.

Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
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/20260515-arm_coresight_path_power_management_improvement-v14-22-f88c4a3ecfe9@arm.com