coresight: fix missing error code when trace ID is invalid

coresight: fix missing error code when trace ID is invalid

When coresight_path_assign_trace_id() cannot assign a valid trace ID,
coresight_enable_sysfs() takes the err_path goto with ret still 0,
returning success to the caller despite no trace session being started.

Change coresight_path_assign_trace_id() to return int, moving the
IS_VALID_CS_TRACE_ID() check inside it so it returns -EINVAL on failure
and 0 on success. Update both callers to propagate this return value
directly instead of inspecting path->trace_id after the call.

Fixes: d87d76d823d1 ("Coresight: Allocate trace ID after building the path")
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Richard Cheng <icheng@nvidia.com>
Signed-off-by: Jie Gan <jie.gan@oss.qualcomm.com>
Reviewed-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260512-fix-trace-id-error-v4-1-eb3de789767a@oss.qualcomm.com