perf trace: Fix exit_group() formatting

perf trace: Fix exit_group() formatting

This doesn't return, so there is no raw_syscalls:sys_exit for it, add
the ending ')', without any return value, since it is void.

Reported-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-vh2mii0g4qlveuc4joufbipu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>