perf cgroup: Remove misplaced __maybe_unused

The 'opt' parameter in parse_cgroups() _is_ used. The original patch
used '__used' that was even more confusing :-)

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 023695d9 ("perf tool: Add cgroup support")
Link: https://lkml.kernel.org/n/tip-4jo2puz0empkoou6bbq460tl@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cgroup.c

@@ -153,7 +153,7 @@ void close_cgroup(struct cgroup_sel *cgrp)
 	}
 }
 
-int parse_cgroups(const struct option *opt __maybe_unused, const char *str,
+int parse_cgroups(const struct option *opt, const char *str,
 		  int unset __maybe_unused)
 {
 	struct perf_evlist *evlist = *(struct perf_evlist **)opt->value;