[CIFS] update limit for snprintf in cifs_construct_tcon

In 34c8790 "Shrink stack space usage in cifs_construct_tcon" we
change the size of the username name buffer from MAX_USERNAME_SIZE
(256) to 28.  This call to snprintf() needs to be updated as well.
Reported by Dan Carpenter.

Reviewed-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -3485,7 +3485,7 @@ cifs_construct_tcon(struct cifs_sb_info *cifs_sb, uid_t fsuid)
 		goto out;
 	}
 
-	snprintf(username, MAX_USERNAME_SIZE, "krb50x%x", fsuid);
+	snprintf(username, sizeof(username), "krb50x%x", fsuid);
 	vol_info->username = username;
 	vol_info->local_nls = cifs_sb->local_nls;
 	vol_info->linux_uid = fsuid;