ubifs: setflags: Don't show error message when vfs_ioc_setflags_prepare() fails

Following process will trigger ubifs_err:
  1. useradd -m freg                                        (Under root)
  2. cd /home/freg && mkdir mp                              (Under freg)
  3. mount -t ubifs /dev/ubi0_0 /home/freg/mp               (Under root)
  4. cd /home/freg && echo 123 > mp/a			    (Under root)
  5. cd mp && chown freg a && chgrp freg a && chmod 777 a   (Under root)
  6. chattr +i a                                            (Under freg)

UBIFS error (ubi0:0 pid 1723): ubifs_ioctl [ubifs]: can't modify inode
65 attributes
chattr: Operation not permitted while setting flags on a

This is not an UBIFS problem, it was caused by task priviliage checking
on file operations. Remove error message printing from kernel just like
other filesystems (eg. ext4), since we already have enough information
from userspace tools.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>