coresight: making cpu index lookup arm64 compliant

Function "get_logical_index()" is not available on arm64.
Instead of adding the function simply using "of_get_cpu_node()" and
comparing the return value with cpu handles yields the same
result.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>