We need to clear FI_NO_PREALLOC flag in error path of f2fs_file_write_iter,
otherwise we will lose the chance to preallocate blocks in latter write()
at one time.

Fixes: dc91de78 ("f2fs: do not preallocate blocks which has wrong buffer")
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>