perf sched: Make sure it frees the usage string

perf sched: Make sure it frees the usage string

The parse_options_subcommand() allocates the usage string based on the
given subcommands.  So it should reach the end of the function to free
the string to prevent memory leaks.

Fixes: 1a5efc9e13f357ab ("libsubcmd: Don't free the usage string")
Reviewed-by: Ian Rogers <irogers@google.com>
Tested-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250703014942.1369397-2-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>