In coresight perf mode, we need to prepare the sink before
starting a session, which is done via set_buffer call back.
We then proceed to enable the tracing. If we fail to start
the session successfully, we leave the sink configuration
unchanged.  In order to make the operation atomic and to
avoid yet another call back to clear the buffer, we get
rid of the "set_buffer" call back and pass the buffer details
via enable() call back to the sink.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>