tracing/uprobes: Pass 'is_return' to traceprobe_parse_probe_arg()

Currently uprobes don't pass is_return to the argument parser so that
it cannot make use of "$retval" fetch method since it only works for
return probes.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

kernel/trace/trace_uprobe.c

@@ -514,7 +514,7 @@ static int create_trace_uprobe(int argc, char **argv)
 
 		/* Parse fetch argument */
 		ret = traceprobe_parse_probe_arg(arg, &tu->tp.size, parg,
-						 false, false);
+						 is_return, false);
 		if (ret) {
 			pr_info("Parse error at argument[%d]. (%d)\n", i, ret);
 			goto error;