perf test pmu: Avoid 2 static path arrays

Avoid two static paths that contributed 8,192 bytes to .bss are only
used duing the perf parse pmu test. This change helps FORTIFY
triggering 2 warnings like:

```
tests/pmu.c: In function ‘test__pmu’:
tests/pmu.c:121:43: error: ‘%s’ directive output may be truncated writing up to 4095 bytes into a region of size 4090 [-Werror=format-truncation=]
  121 |         snprintf(buf, sizeof(buf), "rm -f %s/*\n", dir);
```

So make buf a little larger.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Ross Zwisler <zwisler@chromium.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Yang Jihong <yangjihong1@huawei.com>
Link: https://lore.kernel.org/r/20230526183401.2326121-16-irogers@google.com


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