coresight: Appropriately disable trace bus clocks

coresight: Appropriately disable trace bus clocks

Some CoreSight components have trace bus clocks 'atclk' and are enabled
using clk_prepare_enable().  These clocks are not disabled when modules
exit.

As atclk is optional, use devm_clk_get_optional_enabled() to manage it.
The benefit is the driver model layer can automatically disable and
release clocks.

Check the returned value with IS_ERR() to detect errors but leave the
NULL pointer case if the clock is not found.  And remove the error
handling codes which are no longer needed.

Fixes: d1839e687773 ("coresight: etm: retrieve and handle atclk")
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-v6-5-1dfe10bb3f6f@arm.com