nilfs2: mark S_NOATIME on inodes only if NOATIME attribute is set

At present, nilfs marks S_NOATIME flag on all inodes.  This restricts
nilfs_set_inode_flags function so that it marks S_NOATIME only if a
given inode has an FS_NOATIME_FL flag.

Although nilfs does not support atime yet, touch_atime() still safely
returns on IS_NOATIME check since MS_NOATIME is always set on sb.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>