perf tests: Make leader sampling test work without branch event

perf tests: Make leader sampling test work without branch event

Arm a57 only has speculative branch events so this test fails there. The
test doesn't depend on branch instructions so change it to instructions
which is pretty much guaranteed to be everywhere. The
test_branch_counter() test above already tests for the existence of the
branches event and skips if its not present.

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
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: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Veronika Molnarova <vmolnaro@redhat.com>
Link: https://lore.kernel.org/r/20241115161600.228994-1-james.clark@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>