f2fs: no need to initialize zero value for GFP_F2FS_ZERO

Since f2fs_inode_info is allocated with flag GFP_F2FS_ZERO, so we do not
need to initialize zero value for its member any more.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>