ftrace: Fix char print issue in print_ip_ins()

When ftrace bug happened, following log shows every hex data in
problematic ip address:
  actual:   ffffffe8:6b:ffffffd9:01:21

But so many 'f's seem a little confusing, and that is because format
'%x' being used to print signed chars in array 'ins'. As suggested
by Joe, change to use format "%*phC" to print array 'ins'.

After this patch, the log is like:
  actual:   e8:6b:d9:01:21

Link: https://lkml.kernel.org/r/20221011120352.1878494-1-zhengyejian1@huawei.com

Fixes: 6c14133d ("ftrace: Do not blindly read the ip address in ftrace_bug()")
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -2028,7 +2028,6 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
 static void print_ip_ins(const char *fmt, const unsigned char *p)
 {
 	char ins[MCOUNT_INSN_SIZE];
-	int i;
 
 	if (copy_from_kernel_nofault(ins, p, MCOUNT_INSN_SIZE)) {
 		printk(KERN_CONT "%s[FAULT] %px\n", fmt, p);
@@ -2036,9 +2035,7 @@ static void print_ip_ins(const char *fmt, const unsigned char *p)
 	}
 
 	printk(KERN_CONT "%s", fmt);
-
-	for (i = 0; i < MCOUNT_INSN_SIZE; i++)
-		printk(KERN_CONT "%s%02x", i ? ":" : "", ins[i]);
+	pr_cont("%*phC", MCOUNT_INSN_SIZE, ins);
 }
 
 enum ftrace_bug_type ftrace_bug_type;