coresight: etm4x: Fix mis-usage of nr_resource in sysfs interface

coresight: etm4x: Fix mis-usage of nr_resource in sysfs interface

The member @nr_resource represents how many resource selector pairs,
and the pair 0 is always implemented and reserved.
So let's multiply by 2 when resetting the selector configuration.
And also update the validation of the input @idx.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Jonathan Zhou <jonathan.zhouwen@huawei.com>
[Fixed typographical error in changelog, added stable]
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200916191737.4001561-16-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>