perf stream: Use evsel rather than evsel->idx

perf stream: Use evsel rather than evsel->idx

An evsel idx may not be stable due to sorting, evlist removal,
etc. Avoid use of the idx where the evsel itself can be used to avoid
these problems.

Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Chen Ni <nichen@iscas.ac.cn>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241114230713.330701-2-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>