perf tools: Don't allow empty argument for field-separator

Both 'perf diff' and 'perf mem' have 'field-separator' option, which
causes segfault if passed with empty string. This patch uses previously
introduced 'OPT_STRING_NOEMPTY' option macro to prevent fault.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: pi3orama@163.com
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/1426820272-23302-1-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-mem.c b/tools/perf/builtin-mem.c
index 46c6931..b4dcf0b 100644
--- a/tools/perf/builtin-mem.c
+++ b/tools/perf/builtin-mem.c
@@ -286,7 +286,7 @@
 		   "input file name"),
 	OPT_STRING('C', "cpu", &mem.cpu_list, "cpu",
 		   "list of cpus to profile"),
-	OPT_STRING('x', "field-separator", &symbol_conf.field_sep,
+	OPT_STRING_NOEMPTY('x', "field-separator", &symbol_conf.field_sep,
 		   "separator",
 		   "separator for columns, no spaces will be added"
 		   " between columns '.' is reserved."),