9p: Fix v9fs show_options

Add the delimiter ',' before the options when they are passed
and check if no option parameters are passed to prevent displaying
NULL in /proc/mounts.

Signed-off-by: Abhishek Kulkarni <adkulkar@umail.iu.edu>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

fs/9p/vfs_super.c

@@ -220,8 +220,8 @@ static void v9fs_kill_super(struct super_block *s)
 static int v9fs_show_options(struct seq_file *m, struct vfsmount *mnt)
 {
 	struct v9fs_session_info *v9ses = mnt->mnt_sb->s_fs_info;
-
-	seq_printf(m, "%s", v9ses->options);
+	if (v9ses->options != NULL)
+		seq_printf(m, ",%s", v9ses->options);
 	return 0;
 }