perf report: Fix misleading help message about --demangle

perf report: Fix misleading help message about --demangle

The wrong help message may mislead users. This commit fixes it.

Fixes: 328ccdace8855289 ("perf report: Add --no-demangle option")
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Jiachen Zhang <me@jcix.top>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.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.kim@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250109152220.1869581-1-me@jcix.top
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>