perf probe: Set default kprobe group name if it is not given

perf probe: Set default kprobe group name if it is not given

Set kprobe group name as "probe" if it is not given.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Hemant Kumar <hemant@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20160426090413.11891.95640.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>