perf probe: Check return value of strlist__add() for -ENOMEM

strlist__add() may fail with -ENOMEM. Check it and give debugging hint
in advance.

Signed-off-by: He Zhe <zhe.he@windriver.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lore.kernel.org/lkml/1582727404-180095-1-git-send-email-zhe.he@windriver.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>