tracing: probes: Fix to zero initialize a local variable

Fix to initialize 'val' local variable with zero.
Dan reported that Smatch static code checker reports an error that a local
'val' variable needs to be initialized. Actually, the 'val' is expected to
be initialized by FETCH_OP_ARG in the same loop, but it is not obvious. So
initialize it with zero.

Link: https://lore.kernel.org/all/171092223833.237219.17304490075697026697.stgit@devnote2/Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/b010488e-68aa-407c-add0-3e059254aaa0@moroto.mountain/
Fixes: 25f00e40 ("tracing/probes: Support $argN in return probe (kprobe and fprobe)")
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

kernel/trace/trace_probe.c

@@ -839,7 +839,7 @@ int traceprobe_get_entry_data_size(struct trace_probe *tp)
 void store_trace_entry_data(void *edata, struct trace_probe *tp, struct pt_regs *regs)
 {
 	struct probe_entry_arg *earg = tp->entry_arg;
-	unsigned long val;
+	unsigned long val = 0;
 	int i;
 
 	if (!earg)