perf cs-etm: Fix wrong return values in error path

Function cs_etm__mem_access() is supposed to return a u32 but the error
path returns negative values at a couple of places, something that really
throws off the clients using it.  Fix the situation by return '0'.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki K Poulouse <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20190212171618.25355-4-mathieu.poirier@linaro.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>