f2fs: clean up parameter of f2fs_allocate_data_block()

Use validation of @fio to inidcate whether caller want to serialize IOs
in io.io_list or not, then @add_list will be redundant, remove it.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>