coresight: etm4x: Fix missing trctraceidr file in sysfs

The trace ID patchset adjusted the handling of the TRCTRACEIDR register
sysfs to allocate on read.

Although this was initally correct, the final version of the patch series
introduced an error which resulted in the mgmt/trctraceidr file in sysfs
not being visible.

This patch fixes that issue.

Fixes: df487120 ("coresight: etm4x: Update ETM4 driver to use Trace ID API")
Reported-by: Junhao He <hejunhao3@huawei.com>
Link: https://lists.linaro.org/archives/list/coresight@lists.linaro.org/thread/KK3CVVMRHJWVUORKMFJRSXYCEDFKENQJ/


Signed-off-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230512133054.235073-1-mike.leach@linaro.org